I have been playing a game on a Large map with a bunch of AIs.  One, a custom faction named "Obnoxious Dinner Guests" quickly jumped out to a sizable lead and has held on to it as the game has continued.  However, I have been catching up over the last 100 turns or so.

Imagine my surprise when I loaded up my latest save to find that the Obnoxious Dinner Guests were no longer present in my game!

One save they're there:

http://dl.dropbox.com/u/6130973/FE/FactionIsThere.EleSav

The next (and all the autosaves that were with it -- ~15 turns later), they're gone like they never existed:

http://dl.dropbox.com/u/6130973/FE/FactionIsGone.EleSav

Even the places where they had cities are just fertile land.  It's like they resigned, but I feel like I would have noticed the most powerful faction in the game quitting or dying.