No, there won’t be a 3rd party.
What there will be is a shift among GOP voters. Any GOP candidate that is seen as a “politician” (Romney, Pawlenty, even Perry) will be dead as voters realize they can’t even trust the conservative politicians to stand firm.
Bachmann, Cain, even Paul will pick up significant support.
I want nothing to do with the GOP. To be in the party is to be compromised. What do they have to do hit you in the head with a bat? In person? Not me. I would rather go down fighting if I go down.