When Webb drops, I would expect virtually all of his supporters to jump to Dean.  So Dean could easily fall short on the first ballot but win once you add in the Colorado and African-American delegates who prefer to show their support for Webb on the first ballot.

Since Webb endorsed Dean for President, I wouldn't at all be surprised if he endorsed Dean for DNC after he is eliminated.  If it goes past the first ballot, I would expect the order of elimination to be:

Leland
Roemer
Webb

Also, since the voting process is to drop the lowest candidate each round, who's to say that some of Rosenberg and Fowler's supporters -- in theory people who want reform -- wouldn't vote for Dean once their guy is out?