So good!
You could consider add a function which will backup permission files automatically.And if need,admins could undo some illegal actions by ops with a command to rewrite permission file(means cover the changed permission files into the latest safe backup)
Also,I think it is very important to make such a function that make plugin comparethe permission or op changes,which means when someone become OP or have an extra permission,plugin will automatically take down these actions and save them in a log file.