About that serious bug you mention, I haven't modded CKIII but I have a wee bit of an understanding of how it works (and am trying to learn more) and I've been trying to work out things like this in particular, both in terms of landed domiciles and and in terms of information being stored for longer than it usually exists. Would it be possible to create a (mechanically null) character modifier or trait on the player character (itself with properties changed by each present building and ongoing building process) to store the current state of their estate?

If so, would it be possible to detect inheritance-from-vassal and automatically read that trait in order to rebuild (as in, recreate that exact estate, albeit with different building positions) in such a situation? So, buildings change trait, trait persists on character, vassal death causes event, event reads trait, event creates "new" domicile from trait, player wonders why their buildings are in the wrong positions.

To be fair I'd guess that this rebuild, if possible, would have to freely restart the construction of anything currently being constructed when the inheritance happens (since I'm guessing the current progress of that construction would be difficult to store), but a cheeky little "construction delays" event would presumably be preferable to the disaster of losing your entire domicile.

I don't know if this would be a prohibitive amount of work, or even functional, but I thought I should mention it! I also don't know the proper language for modding just yet so my terminology might be totally wrong. Sorry about that if so!