It probably will fire up Dean's few remaining supporters, but I'd predict there is absolutely no way it will result in him getting the nomination.
The overwhelming majority of Dems have concluded that he is not presidential material and would get hammered by W.
If Kerry stumbles look for Edwards, Hillary or someone else to jump in. There will be no second act for Dean.
Someone correct me if I'm wrong, but I don't think they can jump into the race this late in the game. I imagine ballots are already printed up for, and the deadline has passed in all the super tuesday states. I suppose someone could start a write in movement, but that seems difficult considering the average intelligence of a democrat voter (remember florida 2000).
Perhaps someone who knows the rules regarding primary elections could answer this one way or the other...