I'm sorry to have been away from this thread and missed follow-up questions from ndejs and MillerWins.
The XML file is not critical in restoring your library. If you do find a file called iTunes Music Library.xml, you can rename it, delete it, or drag it out of the iTunes folder. But if you don't find such a file, that's okay too. Once iTunes is working again, it will generate a new XML file automatically.
The master file that stores all the information about your iTunes library is the one called "iTunes Library.itl" -- and this is the file that seems to be getting corrupted by a glitch in the latest releases of the iTunes app. What we need to do is find an earlier, saved version of this file from before the recent iTunes update, and use it to replace the corrupted version. The best-case scenario is probably a Time Machine backup from just before you installed the latest iTunes. The next best is a file from the Previous iTunes Library folder -- probably the most recent one, as long as it was created before the problem started.
If this solution works for you -- and I truly hope it does! -- you just need to remember that any files or playlists added very recently (between the last backup and right now) will need to be re-imported or re-created.