If McCain wins, I see two possibilities:
The GOP crumbles. Fusionism breaks down. Social conservatives break away from the GOP, leaving free marketers and strong defense advocates holding the ball. The religious right moves along to the ironically named Constitution Party in order to pursue their dreams of a Christian Theocracy. That's okay, though, as without the religious right, independent social moderates who want neither high taxes, nor gov't sponsored religious aid programs, move right in and make themselves comfy. With a much diminished independent vote, the Democrats lose their footing and gradually sink from power until the die-hard leftists are purged from their ranks. Once this occurs Republicans and Democrats find new middle ground and honest-to-god reasonable compormise. A new golden age ensues. The United States is reborn as a land of opportunity, liberty, and happiness. The religious right and the leftists get dragged along, kicking and whining, and generally ignored.
The other possibility is the GOP holds together until the post-McCain years, then fire up the rhetoric machine again, beating the same old drum and dead horse as always: abortion, protection of marriage, the family, etc., etc... until everyone is sick of it and loses interest. The Democrats win the following 8-16 years, the US as we know it ends, replaced by an inferno of sky-high taxes, poor health care, horrendous energy prices, a dwindling economy, and societal collapse.
If Obama wins, I figure that we just get a jump start on the latter possibility.
Not that I agree with the wacky alternative-lifestyle crowd, but as long as they stay out of my business, live and let live. Abortion should be very highly regulated, but no-fault / no-blame adoption should be encouraged. The family is strong when the economy is strong, and when personal responsibility is emphasized over gov't assistance. Personal responsibility starts with the rewards of one's efforts going into ones pockets, not the coffers of gov't.