Would setting up drive mirroring not reduce the possibility of rogue Admins? Basically, when a file on the master drive get's updated, the old copy is written to a second drive. When a file on the origional gets deleted, a copy stays on the second drive. Keep the second drive's access password protected, such that William only knows the key, and you always have a reasonably up-to-date back-up. Worst case scenario with a rogue admin would be the last post to each thread going walkies after a few hours of the board being down... Updates may also be reversed, but it's far better than re-building veirtually from scratch, and less time-consuming I imagine?
That's not drive mirroring, by definition a mirror reflects a 'copy' of the data and is used to protect against data loss due to hardware failures. You're talking more about a version control system really.
Daily full back-ups, and even more regular incremental backups would be the simplest and easiest safeguard.