What is your problem with that?
Once created / assigned you should not delete users. At least not easily.
Local / global lock or validity is sufficient. Removing all authorizations (also profiles!) also achieves the same (bar program vulnerabilities which require no authorizations).
-> you should not delete users, which is functionally equivalent to removing system assignments.
Or are you really sure that your intention is to delete the user ID completely?
Cheers,
Julius