Hmm, well, since the message has been basically useless for debugging for a decade, and the historical figure stores most of the important bits (skills, artifacts, relationships, etc), I'm going to try a new approach and have the game recreate the unit, and use your save as a test case. This might fail spectacularly, so no promises! Affected units would lose their non-artifact items, and perhaps certain crucial information about pets, and many of their wounds and all of their thoughts and possibly rooms and property and so forth (to the extent that wasn't broken already), but presumably that's better than destroying the entire world. However, it might also break the game in unexpected ways; I'll maintain an error log with the exact unit file that failed and see if that helps.
Noting again that this enterprise might be doomed and I just end up reverting at the end of today, but if it works, as long as the error log is there, hopefully this won't create a bunch of tricky-to-diagnose false positive bug reports.
Not that I'll be able to help your world for much longer... 5 GB of mem used almost blew out my computer, he he he.
edit: looks like it was a goblin bard from unit-165.dat... which wasn't there. So it doesn't seem to be a corrupt file, but rather a missing file (or the hf had a file assigned incorrectly.) I can use that as a data point, anyway. In any case, the next version creates a new body/items for the bard and they show up properly... can't say there won't be some sort of catastrophic collapse, but the save should be usable in the next version.