I think at this point Huckabee becomes the VP for whoever wins on the Republican side (unless its Paul in some massive upset).
By having millions left to spend, I actually think Paul can outlast everyone except Romney if the race remains open. But I think Huckabee will drop out, and I'm all but sure Guiliani will drop out if he comes in a distant second or third in Florida, since the bad-press making him look like a complete tool for waiting so long to campaign heavily will be enormous. He's obviously still in it with a win in Florida, although without money and unlikely to win even NY, CT and NJ.
Paul can survive by targeting places like Nevada and Lousiana (tonight) where no one is really competing, and costing other candidates delegates. If he mounts double digits in most states, he can probably run as a third party candidate, and pretty much assure a split among Republicans between the Goldwater guys vs. Neocons guys. If Bloomberg ran he'd hurt both moderate support for both parties as well.
I don't believe Paul can win the general election, but if he keeps fighting through November he is laying the seeds for a real Libertarian Revolution as his movement will have touched millions, and among them will be a refined, younger, attractive candidate. Its almost as if Paul wins in a sense just by knocking out alot of the former frontrunners.