What happens if

1. Those Democrats win the House? The republic will not collapse. In some respects, having a defined adversary in one or more branches of Congress would probably work to the GOP advantage in some respects. One of the reason that the Democrats have been able to gain ground, at least rhetorically, in this election cycle is that they can plausibly claim that they don't have any say in what is going on in the government. Putting Nancy Pelosi's face on the Congress would probably help George Bush, because I believe that the Democratic party has been essentially laying in the weeds. They don't have to push a specific agenda right now; all they have to do is ostentatiously point out "we're not responsible." And they don't have to explain what their solution is. And not surprisingly, they haven't. A lot of people have decided they aren't going to listen to George Bush any more. But they will listen to Pelosi if she becomes Speaker. And that might be the worst result for the Democrats.
2. The Democrats fail to win? That's actually a more interesting question, since it would represent something approaching an existential crisis for the Party of Government. Things will never be more advantageous than now and the Democrats continue to benefit from an incredible MSM echo chamber and the enconia of the people who buy their ink by the barrel. For the past six years, there has been a relentless drumbeat of bad news that various people have tied, to varying degrees, around the neck of George W. Bush. Bush's approval rating, as we are reminded daily, is something like -3000%. In fact, dead people, animals and most plants hate George W. Bush, too. Yet, somehow, his political party may still end up pulling this out. If your opponent is as universally hated as George W. Bush is purported to be, and you still lose, what does that say about you? If I were a Democrat, I sure wouldn't want to answer that question.