I have my pictures on a share so both me and my wife can use the picture-storage. And therefore I really like IPTC. Of course, my picture-share is backed up in case of crash. But what about the "Defined keywords list". And here is my suggestion.
Make a command that can scan my picture-folder/share and all sub-folders to build all lists again (keywords, categories and more). I would also be acceptable for me if there was a little file following the picture at all time. AS LONG AS IT FOLLOWS THE PICTURE and can be a help to quickly build the database again.

(Seen with "simple" eyes.)
I hope you can use this suggestion.