This is a weird one, but have you ever had a campaign abruptly end because a pet character got killed?
We had an Eberron campaign about a mysterious insanity-causing plague. After a lot of investigation, it turned out it was caused by a formerly-thought-dead leader of the Blood of Vol.
But it turned out that he was dead, and his sickly teen genius daughter had taken over the organization, talking to her father's mummified corpse like a schizo.
Anyway, when we finally caught up with her, she was about to give a long speech from her wheelchair...Until the Barbarian bull-rushed her out of a window, and (I quote):
>"I hold on to her on the way down."
That was pretty much the end of the campaign right there, mostly because there were no more leads to go on and she was clearly important. But the mental image of a Barbarian giving a sickly waif the ol' Atomic Piledriver off the top rope was a pretty funny way to end things.