do myBB have some plugins to restore erased users account?
Once you've deleted a user account it's gone forever. Removed from the database.
Do you have a backup of your forums?
That also goes for any data (posts, threads, etc)
SQL isnt forgiving like windows where everything first moves to a trashcan nor is there an undo cache with php scripts. Once its gone thats it. I have thought about coding some proprietary Undo systems and recycle bins for my admin software. Just not quite sure how to make it universal, maybe with CSV.