It looks like "delete user" was recently enabled for admins and potentially users. Its current iteration is proving to be more problematic than helpful, as it still leaves traces of the account in the database.
This is important to note for name changes, as if the user creates an account with their updated email, and then deletes it, it prevents us from re-using their new email. This is also the case if account admins delete the new user account instead of doing a merge.
Please allow "delete user" to fully delete their account from Smartsheet databases entirely.