I don’t personally think that the data needs to have a fake user by default, and data without a user should be able to be purged upon request but it should absolutely not be done when closing a saved file.
A saved file should restore to the state it was in when it was saved. Period.
If that state was that there are unused data blocks waiting either for a user or to be removed by a purge command, then that is what should come back. It’s what the user expects. It’s what all other programs with similar concepts do.