I think if Romney loses, the GOP will, at a minimum, be reorganized.
More likely, in 2016 (if there are elections), it will be a minor third party with 5% or less of the vote.
The GOP today is basically the democrat party of 2000/2004 (perhaps a little more to the right on economic issues)
By 2016 I could see the GOP competing with today's democratic party on who can be more left.