Do Ron Paul supports still think he has a chance? Where will they go when he's shoved off?
Hard to say. I voted Nader in '00, voted Kucinich in the '04 primary and Kerry in the '04 general. The first two were cases of A) idealism and B) liking the other alternatives so little that I wouldn't have voted for them anyway (bear in mind Dean was already dust by last Super Tuesday), while the last was a case of, all right, this guy's a dick but the alternative is so much worse that I'm going to have to bite the bullet and vote for him anyway. That's kinda what I'm about to do with Obama, though I like him better than Kerry, anyway.
There are lots of contributing factors that could cause someone to stick with Paul or jump ship. Pragmatism plays the biggest role in states where the race is close, obviously; I don't see a hell of a lot of Paul voters in my state deciding "No, I have to go McCain" or "No, I have to go Romney", because they're pretty well assured the #1 and #2 slot, respectively, and Paul voters jumping ship won't change either of those. In states where McCain and Romney are running neck-and-neck, however (or, in the case of independents who are allowed to vote in either party's primary, ones where Clinton and Obama are running neck-and-neck), they may be more tempted to vote a more pragmatic choice.
Course, if Paul dropped out, you'd see more people switching to other, more feasible candidates, but he's got the dough to stick this out and he's here to prove a point, so I'm guessing he'll be around for awhile yet. Like Kucinich in '04.
Then you get the people who are purely Ron Paul supporters, and nothing is going to change that. If he drops out, they may STILL vote for him (note that Richardson's probably going to win the New Mexico primary despite having dropped out weeks ago), or simply stay home; otherwise, they're voting for him, period, and nobody else is even an option. Realistically, I think those people are a minority, but they're definitely out there.
Beyond the primary? Well, he HAS threatened to run as a third-party candidate, and his treatment by Fox News and others clearly shows that he's being shafted by the Republican Party. (Keep in mind he was kept out of the New Hampshire debate despite polling ahead of Giuliani, who was allowed in because Rupert Murdoch loves him so goddamn much. Oh, and if you'll pardon a little schadenfreude, Rupert is very sad right now.) But I doubt that'll ACTUALLY happen.