Edit master.gsav in your save’s directory.
Open some other master.gsav from any other file and manually copy the missing factions, then properly close the braces if any are left unclosed or closed in wrong order.
The actual values are nearly irrelevant (most of them, likes_u and respects_u do have effects), but all fields need to be present.
If that doesn’t work, it may be corrupted overmap file. This one may make the save unrecoverable.
You might still be able to transplant your character into a different world by copying the file that starts with some hashed gibberish and ends with .sav. Just place that file in a different world and it should become playable, but the world will be regenerated.