To begin with: Newt Gingrich never had a chance to be the Republican nominee for president in 2012 or any other year. I'll go back to what I said before his very first collapse back in the spring: he's Sarah Palin without the fanatical supporters but with the marital history of John Edwards. In other words, he has no natural constituency that would stick with him no matter what, Washingtonians don't like or trust him, and there's an opposition research file that's so enormous that he can be attacked effectively by any candidate in any electoral context. The idea that specific campaigning mistakes doomed him is nonsense, as is the idea that he might come back again and "stop Romney in South Carolina and then Florida" on his way to competing seriously for the nomination. He's not a serious contender, and never has been.
In the normal course of things, a Newt Gingrich who finishes a weak fourth or worse today, and then goes on to finish fourth or worse in New Hampshire, would quietly drop out after that. And it may well happen that way.
But I can see another possible future for the disgraced former Speaker. Up to this point, I've compared his campaign to Gary Hart's 1988 "comeback" -- which for a brief time rocketed Hart to the top of the polls, and all sorts of speculation from gullible pundits that perhaps all was forgiven and that he could still compete seriously for the nomination, but which actually just turned out to be the meaningless effects of name recognition and recent media attention. Hart was never a factor, and while there's always the chance that Newt could finish better than it looks in Iowa today, he's never been a plausible nominee.
However, what if he doesn't drop out? Newt is unusually good at attracting national media attention, and so he's not likely to be just completely ignored, especially if we hit a point in the process at which Mitt Romney is close to wrapping it up but isn't quite there yet. And that's when Newt could wind up doing something similar to what Jerry Brown did in 1992. In that year, Brown (who was at that point a washed-up has-been of a politician) was almost completely ignored while Bill Clinton went about wrapping up the nomination. However, late in the day, Brown wound up getting some attention and even won a primary, allowing the press to temporarily pretend that he was a real threat to Clinton's nomination for a week or two.
That's not an unusual role, actually. It's not a lot different from what John McCain got to do it in 2000, although that was much earlier in the process...but it was, similarly, after all the real threats to George W. Bush had been eliminated.
There's no guarantee that Newt will try to do that this time, and even if he tries there's no guarantee that he would succeed; among other things, it probably depends on whether Rick Santorum is able to mount a serious challenge to Romney that lasts beyond Florida.* Mostly just caucus day speculation...it's fun to cast candidates as previous candidates, even if it's not exactly rigorous analysis. Anyway, the bottom line here is that if he thinks it'll sell more books and such, we're may have Newt to kick around for a while longer, even though he's gone from having no chance at the nomination with high poll numbers to no chance at the nomination with, soon, some lousy caucus numbers.
*For maybe the last time: or Rick Perry, if the polls all missed something and he finishes third or better in Iowa and builds on that.