[Supay]

The one issue so far that has been a bit of a pain, was that other users who share the database could hose the library if their pi was to lose a mount and attempt cleanup (they selected the default 'delete' option when the prompt showed).

Not sure if this has been mentioned in the previous posts, but the way I got around this was to create a read-only mysql user for those users' pis, and grant only SELECT access to all tables in their db, except granting ALL access to both the bookmark and files tables.  Been using this for a few weeks now without issues for the most part.  They can still have their own watched status and get regular updates when i update from my end.  One small issue is if a read-only user attempts to refresh certain items, OSMC will die with a sadface, but thats minimal and I just tell them to stop trying to update.

Has anyone else been plagued with other users hosing their library like this?  If so, just wondering how they approached preventing it.

With my children growing and experimenting, this has become an issue for me as well.  I'm about to try the same setup, so hopefully it works.  Will confirm once done!