I think it is fair to say that the next president of the United States has announced (or has a pending announcement). The few stragglers remaining on the GOP side will never see a debate stage and will likely drop out before IA (if they ever get in). As for Webb, he could possibly get into some debates but not sure where he fits in to 2016's Democratic party. He and Chafee can fight over the handful of Dems primary voters who think Hillary is too much of a liberal.
They don't appeal to the same constituency. Chafee I think could do better then a lot of people think by appealing to anti-war and civil libertarian voters.