I know, it's not a very good system, but the site's set up perfectly fine and none of the members want to have admins again. There is still the "superadmin" account, but the password's been lost.
I contemplated giving all users - including guests - full administrative access to the site, and raping the Admin Control Panel (I'm good at that) so no-one could ever change it back. It would've been an interesting experiment.
That's one solution- which unfortunately probably wouldn't be that good of an idea, unless there were methods in place to check changes (like on wikipedia).