You are aware that a game save file is a bit more problematic to work with, then most other databases ?

If we prevent that they could do what you are asking. What will happen if a player is now standing in the same location as a lost thrall was standing in ?

What happens if a player picked up the dropped items of a lost thrall ? Item instances might not have a UID

What happens if someone build over the location of a lost thrall ?

What if the building a thrall was standing on, as been destroyed over the weekend.

What happens if new thralls had replaced the old ones ?

Now image a script automatically handling this, what are the odds of some special case having been forgotten ?