So it looks like the magelo page just transcludes another page (ie. it copies it on to its page). For guilds, that's the page
http://wiki.project1999.com/Special:Magelo/GuildList. If you look at that page you'll see it's also blank.
However, not all of the special magelo pages are broken. If you look at
http://wiki.project1999.com/Magelo_Blue:Ravhin you'll see it still lists all magelos for necromancers (
http://wiki.project1999.com/Special:...ch/Necromancer).
My guess is that no one specifically broke the page (which is why restoring history doesn't help), and that it's a problem in the database with either the number of magelos, or a special character someone added to their magelo.
Either way, unfortunately all of the magelo stuff was created by Ravhin, who no longer plays. Someone could try PMing him, but there's no guarantee he'll respond.
Someone who knows PHP could also try to debug the problem themselves, and they could find the code for the magelo extension in
http://wiki.project1999.com/utils/wikiUtils.php ("Custom Extensions Source" link) ... but without access to the wiki server they'd be doing it with one hand tied behind their back.
Personally I already hurt my brain reading the PHP code for the auction tracker, and I still haven't heard back from the staff about implementing the fix I came up with, plus I'm swamped at work, so I'll have to leave fixing this problem to someone else (
hopefully Ravhin himself).