TPKs are often considered to be a bad ending. That doesn't mean they can't be satisfying, but it's not the "heroes win, roll the fanfare" ending that perhaps people were looking for. So what happens after a TPK with your group? Have you even had one?
In my experience, after the TPK everyone kind of hangs around for a little bit and discusses the game and what happened. If I'm GMing, and the game is ending with the TPK, I'll answer questions folks had and try to give closure. Often people will talk about what caused the TPK, and I've been fortunate enough that in the games I've ended that way everyone believed it was a fair encounter.
Then, after a bit, conversation will start turning to the next game. Are we swapping out GMs? Systems? Game types? Sometimes that conversation doesn't happen until the next day via e-mail, but it's not usually that far behind.
And once that conversation happens, well, the last game is over.
How about with your game?