Closed accounts = deletion of all posts

Aisaka You could make a Deleted Posts forum where all purged posts get moved to when they're "deleted" and just make the category private with only staff able to see it. Not sure if mybb has that feature, another forum software does tho.
I made it so that whenever the user or an admin deletes a post, it lands into the "Archives Posts" section that only admins can see and that was the best of both worlds: users didn't see spam and trash posts and staff still had everything archived just in case.