Surely if the GM invokes this just to be malicious towards the players, they can declare it Discontinuity and find a different GM for next week?
Sure, Rocks Fall, Everyone Dies will almost certainly lead to a change of some sort, but chances are that the different GM will have her own ideas, and won't necessarily want to run the same campaign and/or same characters. For that matter, the players themselves might want to get the bad taste of rock out of their mouths and do something completely different.
But it does happen. Particularly if one of the players wants a gamemaster gone that badly, he might offer to take over the existing campaign just to make sure the other players are in. This troper has seen that happen once to an especially belligerent and unapologetic gamemaster.
