When you delete a user through AUTOFORM DM the user is not deleted from the database since that user is likely linked to various other documents in the archive.
Instead, it changes a key so this user is hidden from the AUTOFORM DM front end. If you have deleted a user account that you need to access again you will need to send a request asking Formpipe to edit your database to retrieve the deleted user.
If you want to disable an account that you may need later, we suggest you disable the account rather than delete it. This is so you can reactivate them from the front end.