Romney, Paul, and Perry have the cash to stick this out for a while. Huntsman, Gingrich, and Santorum don't seem to. By the end of January (IA, NH, SC, FL), we could conceivably be down to a 3-man race.
Romney was always in this for a long-run. Paul has his base. Perry's got the cash still too. Santorum's Iowa rise probably won't carry him to big wins in other states. Huntsman was never "THE" guy, he's always seemed to be single-digit in the polls. I don't think he'll get the spike in interest that everyone from Bachmann to Cain to Santorum got. Gingrich - he's low on the dolla dolla bills y'all, though I think he's still got some support out there, but maybe not enough to really sustain him.
At this point, I can't really see this going ****** March. I think Romney will have this even more secure by then than he does now.
(I've based this stuff on general trends I notice from all the media I take in, so if anybody has other views/info/numbers, please share. I'm open to it

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And this season has been freaking nuts, so things can of course change somewhat wildly.