TPKs are epic fail. They simply shouldn't happen. The encounters should favor the party, the players should retreat when things are going bad, the DM should fudge, the Enemies should capture the PCs.
So if one does occur it's a sign of real trouble. Indeed I've played since OD&D and I don't remember ever having seen one. Though I have seem the majority of the party killed before.
I'd say start up a whole new party of characters.