I see one of two things being the highest liklihood for the GOP:
1) Continual electoral defeat that forces younger, smarter, more contemporary conservatism to rise from the GOP's current ashes. The historic precedent for this is the Tory party in England between the end of John Major (who followed Margerat Thatcher) and Cameron today. If you're interested in seeing that model, check out Cameron and his policies.
2) Hegemony within the GOP remains strong and stupid despite defeats, and it is eclipsed by a new brand that reflects the UK Tories. Think Ron Paul or some variation of libertarianism that coalesces with the ideologues such as the Tories.
If you put a gun to my head today and made me pick one or the other, I pick 2.
I believe the GOP as currently constituted is untenable based on its demographics. It's most popular among a segment of the population that is rapidly shrinking. It's party leader is now for all intents and purposes Rush Limbaugh. It's shut the door on any notion of adaptation. The demographics alone kill it. The inability to recognize, over the last 8 years, what it was doing to itself, combined with the continuing inability to recognize how it is being seen by rational actors, is too much to overcome.
"self-aggrandizing jackass" - it says it right on the label