Testdrive: Recover accidentally deleted windows 10 partition table on dual boot system (not boot partition)

I accidentally deleted most of my windows partition table on my dual boot laptop and am trying to fix/recover the faulty partition table.

I have a dual boot laptop: Ubuntu and Windows. Grub still works (I can boot into Ubuntu).

• Ubuntu 16.10 (incl. boot partition) is located at /dev/sdb
• Windows 10 is located at /dev/sda.

I accidentally deleted most of my windows partition table on dev/sda (stupid mistakes happen). Here is what is left according to fdisk:

$ sudo fdisk -lu /dev/sda
Disk /dev/sda: 465,8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 6CAE9467-2FF5-4DB9-8E72-4321E9061C2A

Device      Start     End Sectors  Size Type
/dev/sda2  923648 1128447  204800  100M EFI System

I can still select Windows from grub, but of course now I just get (German for: Recover, the system must be repared):

From my /boot/grub/grub.cfg on /dev/sdb:

menuentry 'Windows Boot Manager (on /dev/sda2)' --class windows --class os $menuentry_id_option 'osprober-efi-46A6-7D64' {
        insmod part_gpt
        insmod fat
        set root='hd0,gpt2'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  46A6-7D64
        else
          search --no-floppy --fs-uuid --set=root 46A6-7D64
        fi
        chainloader /EFI/Microsoft/Boot/bootmgfw.efi

testdisk results for dev/sda:

TestDisk 7.0, Data Recovery Utility, April 2015
Christophe GRENIER <grenier@cgsecurity.org>
http://www.cgsecurity.org

Disk /dev/sda - 500 GB / 465 GiB - CHS 60801 255 63
     Partition               Start        End    Size in sectors
>P MS Data                     2048     923647     921600
 P MS Data                   923648    1128447     204800 [NO NAME]
 D MS Data                  1161216  975772594  974611379
 D MS Data                974774273  975773696     999424
 D MS Data                975773696  976773119     999424

Structure: Ok.  Use Up/Down Arrow keys to select partition.
Use Left/Right Arrow keys to CHANGE partition characteristics:
                P=Primary  D=Deleted
Keys A: add partition, L: load backup, T: change type, P: list files,
     Enter: to continue
NTFS, blocksize=4096, 471 MB / 450 MiB

After looking inside each partition using P: list files (details below) it seems that:

• partition 1: Recovery. ok to keep?
• partition 2: ok
• partition 3: contains windows10 content
• partition 4: should stay deleted (?)
• partition 5: Recovery. ok to delete?

My questions:

• Should I recover partition 3 (using L: load backup)?
• Should partition 4 remain in status D (deleted)? It seems to be corrupted anyway.
• Should partition 5 remain in status D (deleted)? It contains recovery, but there is already a valid recovery located at partition 1.
• How do I ensure that the grub entry to /dev/sda2 points to the correct location?

Results from testdisk after entering each partition with P:

• Partition 1

     P MS Data                     2048     923647     921600
  Directory /
  
  >dr-xr-xr-x     0     0         0  4-Jun-2016 23:48 .
   dr-xr-xr-x     0     0         0  4-Jun-2016 23:48 ..
   dr-xr-xr-x     0     0         0  4-Jun-2016 23:44 Recovery
   dr-xr-xr-x     0     0         0  1-Jun-2016 14:12 System Volume Information
  

• Partition 2

     P MS Data                   923648    1128447     204800 [NO NAME]
  Directory /
  
  >drwxr-xr-x     0     0         0  2-Jun-2016 07:34 EFI
  

• Partition 3

       MS Data                  1161216  975772594  974611379
  Directory /
  
  >dr-xr-xr-x     0     0         0 10-Feb-2017 01:05 .
   dr-xr-xr-x     0     0         0 10-Feb-2017 01:05 ..
   dr-xr-xr-x     0     0         0 22-Aug-2016 22:54 $GetCurrent
   dr-xr-xr-x     0     0         0  2-Jun-2016 10:40 $Recycle.Bin
   dr-xr-xr-x     0     0         0  8-Nov-2016 18:54 Intel
   dr-xr-xr-x     0     0         0 27-Apr-2016 07:52 Logs
   dr-xr-xr-x     0     0         0 16-Jul-2016 13:47 PerfLogs
   dr-xr-xr-x     0     0         0  2-Feb-2017 23:13 Program Files
   dr-xr-xr-x     0     0         0  2-Feb-2017 23:11 Program Files (x86)
   dr-xr-xr-x     0     0         0 22-Aug-2016 22:59 ProgramData
   dr-xr-xr-x     0     0         0 27-Dec-2016 15:55 Python36
   dr-xr-xr-x     0     0         0 22-Aug-2016 22:38 Recovery
   dr-xr-xr-x     0     0         0 20-Jun-2016 22:03 SQL Server 2000 Sample Databases
   dr-xr-xr-x     0     0         0 21-Jun-2016 20:06 SQLServer2016Media
   dr-xr-xr-x     0     0         0 10-Feb-2017 00:28 System Volume Information
   dr-xr-xr-x     0     0         0 22-Aug-2016 22:44 Users
   dr-xr-xr-x     0     0         0 10-Feb-2017 01:06 Windows
   dr-xr-xr-x     0     0         0 22-Aug-2016 22:54 Windows10Upgrade
   dr-xr-xr-x     0     0         0  5-Oct-2016 19:25 _tmp
   dr-xr-xr-x     0     0         0  4-Jun-2016 22:23 cloud
   dr-xr-xr-x     0     0         0  2-Feb-2017 18:45 projects
   dr-xr-xr-x     0     0         0 24-Jul-2016 14:35 tools
   -r--r--r--     0     0         1 30-Oct-2015 08:18 BOOTNXT
   -r--r--r--     0     0         0 27-Dec-2016 15:55 Python36:Win32App_1
   -r--r--r--     0     0         0 20-Jun-2016 22:03 SQL Server 2000 Sample Databases:Win32App_1
   -r--r--r--     0     0    395268 10-Jul-2015 13:00 bootmgr
   -r--r--r--     0     0 2550136832 10-Feb-2017 01:07 pagefile.sys
   -r--r--r--     0     0  16777216 10-Feb-2017 01:07 swapfile.sys
  

• Partition 4

       MS Data                974774273  975773696     999424
  
  Can't open filesystem. Filesystem seems damaged.
  

• Partition 5

       MS Data                975773696  976773119     999424
  Directory /
  
  >dr-xr-xr-x     0     0         0 18-Nov-2016 21:26 .
   dr-xr-xr-x     0     0         0 18-Nov-2016 21:26 ..
   dr-xr-xr-x     0     0         0 22-Aug-2016 23:36 Recovery
   dr-xr-xr-x     0     0         0  4-Jun-2016 22:49 System Volume Information
  

testdisk.log:

Thu Feb 16 20:46:55 2017
Command line: TestDisk

TestDisk 7.0, Data Recovery Utility, April 2015
Christophe GRENIER <grenier@cgsecurity.org>
http://www.cgsecurity.org
OS: Linux, kernel 4.8.0-37-generic (#39-Ubuntu SMP Thu Jan 26 02:27:07 UTC 2017) x86_64
Compiler: GCC 5.3
ext2fs lib: 1.43.3, ntfs lib: libntfs-3g, reiserfs lib: none, ewf lib: none, curses lib: ncurses 6.0
/dev/sda: LBA, HPA, LBA48, DCO support
/dev/sda: size       976773168 sectors
/dev/sda: user_max   976773168 sectors
/dev/sda: native_max 976773168 sectors
/dev/sda: dco        976773168 sectors
/dev/sdb: LBA, HPA, LBA48, DCO support
/dev/sdb: size       976773168 sectors
/dev/sdb: user_max   976773168 sectors
/dev/sdb: native_max 976773168 sectors
/dev/sdb: dco        976773168 sectors
Warning: can't get size for Disk /dev/mapper/control - 0 B - 0 sectors, sector size=512
Hard disk list
Disk /dev/sda - 500 GB / 465 GiB - CHS 60801 255 63, sector size=512 - Samsung SSD 850 EVO 500GB, S/N:S1YCNXAGB00962X, FW:EMT02B6Q
Disk /dev/sdb - 500 GB / 465 GiB - CHS 60801 255 63, sector size=512 - Samsung SSD 850 EVO M.2 500GB, S/N:S24CNXAH208296N, FW:EMT21B6Q

Partition table type (auto): EFI GPT
Disk /dev/sda - 500 GB / 465 GiB - Samsung SSD 850 EVO 500GB
Partition table type: EFI GPT

Analyse Disk /dev/sda - 500 GB / 465 GiB - CHS 60801 255 63
hdr_size=92
hdr_lba_self=1
hdr_lba_alt=976773167 (expected 976773167)
hdr_lba_start=34
hdr_lba_end=976773134
hdr_lba_table=2
hdr_entries=128
hdr_entsz=128
Current partition structure:
 2 P EFI System                923648    1128447     204800 [EFI system partition]

search_part()
Disk /dev/sda - 500 GB / 465 GiB - CHS 60801 255 63
NTFS at 0/32/33
filesystem size           921600
sectors_per_cluster       8
mft_lcn                   38400
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
NTFS part_offset=1048576, part_size=471859200, sector_size=512
NTFS partition cannot be added (part_offset<part_size).
NTFS at 0/32/33
filesystem size           921600
sectors_per_cluster       8
mft_lcn                   38400
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
     MS Data                     2048     923647     921600
     NTFS, blocksize=4096, 471 MB / 450 MiB
FAT32 at 57/126/6
FAT1 : 6654-7422
FAT2 : 7423-8191
start_rootdir : 8192 root cluster : 2
Data : 8192-204799
sectors : 204800
cluster_size : 2
no_of_cluster : 98304 (2 - 98305)
fat_length 769 calculated 769
set_FAT_info: name from BS used

FAT32 at 57/126/6
     MS Data                   923648    1128447     204800 [NO NAME]
     FAT32, blocksize=1024, 104 MB / 100 MiB
NTFS at 72/72/1
filesystem size           974611379
sectors_per_cluster       8
mft_lcn                   786432
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
NTFS part_offset=594542592, part_size=499001026048, sector_size=512
NTFS partition cannot be added (part_offset<part_size).
NTFS at 72/72/1
filesystem size           974611379
sectors_per_cluster       8
mft_lcn                   786432
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
     MS Data                  1161216  975772594  974611379
     NTFS, blocksize=4096, 499 GB / 464 GiB
NTFS at 60739/26/24
filesystem size           999424
sectors_per_cluster       8
mft_lcn                   41642
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
     MS Data                974774273  975773696     999424
     NTFS found using backup sector, blocksize=4096, 511 MB / 488 MiB
NTFS at 60739/26/24
filesystem size           999424
sectors_per_cluster       8
mft_lcn                   41642
mftmirr_lcn               2
clusters_per_mft_record   -10
clusters_per_index_record 1
     MS Data                975773696  976773119     999424
     NTFS, blocksize=4096, 511 MB / 488 MiB

Results
   P MS Data                     2048     923647     921600
     NTFS, blocksize=4096, 471 MB / 450 MiB
   P MS Data                   923648    1128447     204800 [NO NAME]
     FAT32, blocksize=1024, 104 MB / 100 MiB
     MS Data                  1161216  975772594  974611379
     NTFS, blocksize=4096, 499 GB / 464 GiB
     MS Data                974774273  975773696     999424
     NTFS found using backup sector, blocksize=4096, 511 MB / 488 MiB
     MS Data                975773696  976773119     999424
     NTFS, blocksize=4096, 511 MB / 488 MiB

Hint for advanced users. dmsetup may be used if you prefer to avoid to rewrite the partition table for the moment:
echo "0 921600 linear /dev/sda 2048" | dmsetup create test0
echo "0 204800 linear /dev/sda 923648" | dmsetup create test1
echo "0 974611379 linear /dev/sda 1161216" | dmsetup create test2
echo "0 999424 linear /dev/sda 974774273" | dmsetup create test3
echo "0 999424 linear /dev/sda 975773696" | dmsetup create test4
ntfs_device_testdisk_io_ioctl() unimplemented


dir_partition inode=5
   P MS Data                     2048     923647     921600
     NTFS, blocksize=4096, 471 MB / 450 MiB
Directory /
       5 dr-xr-xr-x     0      0         0  4-Jun-2016 23:48 .
       5 dr-xr-xr-x     0      0         0  4-Jun-2016 23:48 ..
      37 dr-xr-xr-x     0      0         0  4-Jun-2016 23:44 Recovery
      35 dr-xr-xr-x     0      0         0  1-Jun-2016 14:12 System Volume Information


dir_partition inode=0
   P MS Data                   923648    1128447     204800 [NO NAME]
     FAT32, blocksize=1024, 104 MB / 100 MiB
FAT: cluster=2(0x2), pos=931840
Directory /
       3 drwxr-xr-x     0      0         0  2-Jun-2016 07:34 EFI
ntfs_device_testdisk_io_ioctl() unimplemented


dir_partition inodentfs_mst_post_read_fixup_warn: magic: 0x00000000  size: 1024   usa_ofs: 0  usa_count: 65535: Invalid argument
Record 0 has no FILE magic (0x0)
Failed to load $MFT: Input/output error
ntfs_mst_post_read_fixup_warn: magic: 0x00000000  size: 1024   usa_ofs: 0  usa_count: 65535: Invalid argument
Record 0 has no FILE magic (0x0)
Failed to load $MFT: Input/output error
=5
     MS Data                  1161216  975772594  974611379
     NTFS, blocksize=4096, 499 GB / 464 GiB
Directory /
       5 dr-xr-xr-x     0      0         0 10-Feb-2017 01:05 .
       5 dr-xr-xr-x     0      0         0 10-Feb-2017 01:05 ..
     132 dr-xr-xr-x     0      0         0 22-Aug-2016 22:54 $GetCurrent
      63 dr-xr-xr-x     0      0         0  2-Jun-2016 10:40 $Recycle.Bin
   86499 dr-xr-xr-x     0      0         0  8-Nov-2016 18:54 Intel
  135457 dr-xr-xr-x     0      0         0 27-Apr-2016 07:52 Logs
  184781 dr-xr-xr-x     0      0         0 16-Jul-2016 13:47 PerfLogs
  184785 dr-xr-xr-x     0      0         0  2-Feb-2017 23:13 Program Files
  192329 dr-xr-xr-x     0      0         0  2-Feb-2017 23:11 Program Files (x86)
  192466 dr-xr-xr-x     0      0         0 22-Aug-2016 22:59 ProgramData
  279327 dr-xr-xr-x     0      0         0 27-Dec-2016 15:55 Python36
  174888 dr-xr-xr-x     0      0         0 22-Aug-2016 22:38 Recovery
  546406 dr-xr-xr-x     0      0         0 20-Jun-2016 22:03 SQL Server 2000 Sample Databases
  210433 dr-xr-xr-x     0      0         0 21-Jun-2016 20:06 SQLServer2016Media
   82311 dr-xr-xr-x     0      0         0 10-Feb-2017 00:28 System Volume Information
  192686 dr-xr-xr-x     0      0         0 22-Aug-2016 22:44 Users
  193184 dr-xr-xr-x     0      0         0 10-Feb-2017 01:06 Windows
   17780 dr-xr-xr-x     0      0         0 22-Aug-2016 22:54 Windows10Upgrade
  136591 dr-xr-xr-x     0      0         0  5-Oct-2016 19:25 _tmp
     463 dr-xr-xr-x     0      0         0  4-Jun-2016 22:23 cloud
  170100 dr-xr-xr-x     0      0         0  2-Feb-2017 18:45 projects
     300 dr-xr-xr-x     0      0         0 24-Jul-2016 14:35 tools
  389125 -r--r--r--     0      0         1 30-Oct-2015 08:18 BOOTNXT
  279327 -r--r--r--     0      0         0 27-Dec-2016 15:55 Python36:Win32App_1
  546406 -r--r--r--     0      0         0 20-Jun-2016 22:03 SQL Server 2000 Sample Databases:Win32App_1
   19844 -r--r--r--     0      0    395268 10-Jul-2015 13:00 bootmgr
      34 -r--r--r--     0      0 2550136832 10-Feb-2017 01:07 pagefile.sys
   82325 -r--r--r--     0      0  16777216 10-Feb-2017 01:07 swapfile.sys
ntfs_device_testdisk_io_ioctl() unimplemented
ntfs_device_testdisk_io_ioctl() unimplemented

     MS Data                974774273  975773696     999424
     NTFS found using backup sector, blocksize=4096, 511 MB / 488 MiB
Can't open filesystem. Filesystem seems damaged.
ntfs_device_testdisk_io_ioctl() unimplemented


dir_partition inode=5
     MS Data                975773696  976773119     999424
     NTFS, blocksize=4096, 511 MB / 488 MiB
Directory /
       5 dr-xr-xr-x     0      0         0 18-Nov-2016 21:26 .
       5 dr-xr-xr-x     0      0         0 18-Nov-2016 21:26 ..
      35 dr-xr-xr-x     0      0         0 22-Aug-2016 23:36 Recovery
      40 dr-xr-xr-x     0      0         0  4-Jun-2016 22:49 System Volume Information

interface_write()
 1 P MS Data                     2048     923647     921600
 2 P MS Data                   923648    1128447     204800 [NO NAME]
simulate write!

TestDisk exited normally.