What I'm most interested in is what will happen when they do implode. The US Constitution all but guarantees a two-party system; at the same time, we have at least half a dozen major ideological strains at the moment:
-The Religious Right, of course, socially conservative, opposed to abortion and gay marriage, often anti-science, and economically on the right;
-The plutocrats, economically pro-corporatist, but indifferent on some social issues and even progressive on a few, notably immigration (though for the wrong reasons);
-The libertarians, economically on the right but generally anti-corporatist, and socially liberal;
-The classic Democrat, liberal on social issues and center-left to left economically;
-The moderate conservative, a rare breed in Washington but quite common in the electorate. Generally center to center-right economically, and center-right to center-left socially. The best example is probably Michael Bloomsburg. Shades into "classic Democrat" as you look at most self-described moderates.
-The socially conservative but economically leftist voter. Generally speaking, we call these African-Americans, who have historically fit here and have been the only major group to fit here for a while, although some Hispanics and urban white evangelical Christians fit here too. There's also some overlap with the classic Democrats here, too, especially with Catholics, many of whom tend to be fairly liberal but are pro-life.
And that's just the main ones off the top of my head! The problem is that there's only two parties, though, so inevitably there will be inter-party conflicts.
If the Republicans implode, the Religious Right, plutocrats, and some libertarians will suddenly have to reshuffle. We could see a return to the libertarian-ish/populist setup we had at the turn of the century, where the social conservatives are also the fiscal liberals (in which case the left-wing evangelicals will swallow up the Religious Right); or one or more of these groups might become marginalized in Washington, like the moderate conservatives are now. (I'd put my bet on the Religious Right, long-term, for this to happen.)
The problem is that the implosion is going to be a question of when, not if. There are several issues that could divide the GOP irreparably like slavery did the Whigs; I'd put my money on gay marriage.