FileVault2 boot volume corrupt after partition deletion
The partition map seems valid and no important small partition has been deleted (maybe one less important EFI or Apple_Boot partition between partition 5 and 6 - the other gaps of unallocated disk space are too small to contain a useful partition e.g. 1648 blocks = ~844 kB). 

Partition 2 and 3 of disk0 got the wrong partition type though - the encrypted partition/data shouldn't be lost. Partition 3 has the typical size of a pre-APFS recovery partition (1269536 blocks) and partition 2 probably is the FV2 partition. The proper type of a recovery partition is 426F6F74-0000-11AA-AA11-00306543ECAC and the proper type of a CoreStorage partition (the base of FV2) is 53746F72-6167-11AA-AA11-00306543ECAC (instead of FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF).

Boot to Internet Recovery Mode or another external boot drive and modify the partition types with gpt.


Boot to Internet Recovery Mode
Get the details:

diskutil list


Below I assume the internal 500 GB SSD has the device identifier disk0

gpt -r show disk0

Remove partition 2 and 3:

diskutil umountDisk disk0
gpt remove -i 3 disk0
diskutil umountDisk disk0
gpt remove -i 2 disk0

Re-add partition 2 and 3 with proper types:

diskutil umountDisk disk0
gpt add -i 3 -b 814312048 -s 1269536 -t 426F6F74-0000-11AA-AA11-00306543ECAC disk0
diskutil umountDisk disk0
gpt add -i 2 -b 409640 -s 813902408 -t 53746F72-6167-11AA-AA11-00306543ECAC disk0

After adding partition 2 with gpt you will probably be asked to enter a passphrase
If not unlock the FV2 volume with:

diskutil cs list
diskutil cs unlockVolume lvUUID #lvUUID: the UUID of the Logical Volume

Verify disk and volume

diskutil verifyDisk disk0
diskutil list #get the device identifier of the mounted FV volume (probably in the upper tens: disk17 or disk18)
diskutil verifyVolume diskX #with diskX: the device identifier of the mounted FV volume