To clarify: Google isn't deleting these files. They're just "restricted", which as far as I can tell means they can't be shared publicly. It's triggering the mechanism to prevent people from using Google Drive as a file sharing service for copyrighted works. I think owners can still access their own files just fine.
That said, I agree 100% that you shouldn't rely on a single point of failure for any backup. Data must be in at least two places.