The GOP would be destroyed.
Unless political debate becomes useless in this country and gets cut off in favor of conservative/reactionary thought, that's pretty much the consensus at this point of what will happen anyway. The question is whether they either become a 45% minority (like they used to be before 1979) or a 49.9% minority (like the dems were after 1979).
don't get too cocky...as the war in iraq turns around, so will the GOP's chances in 2008. the dems are already shying away from criticizing the war and are talking more about domestic issues.