OK. Looks like Kerry, Edwards (!), Dean, Gep, Other.
Gep will drop out, removing the Democrats' least viable major candidate, as the GOP would not even had to caricature him to call him a protectionist in the pockets of the special interests (unions). I don't have a good sense of the man, who seems generally decent and honorable, so I can't predict if he'll endorse anyone. The sensible thing would be to hold off, but at moments like this personal feelings can swing it.
Kerry and Edwards get a boost to New Hampshire. Kerry can now survive a (small) loss in his back yard. Edwards gets Big Mo and a huge increase in news coverage. Dean is wounded but not fatally. Coming in anything worse than a close second in New Hampshire would be major trauma time.
The biggest loser is the GOP. Not only are they deprived of a great target, but they have to spend more on opposition research for longer as there are so many targets.
The biggest question mark is whether the non-Edwards candidates will decide that Iowa is different from the rest of the USA, or if they will read Edwards's strength as a strong lesson that it does NOT pay to go negative against other Democrats. Here's hoping.
Update: See also my second take.