His legislative history shows that he's goal oriented, it's why he got that nickname (amendment king, iirc). I think he's under no illusions about what would happen to the people he views himself as working for if the Republicans win.

I'm quite certain that he will take it as far as he can so as to continue to affect the debate, and then accede and tell his people to vote for the democrat, being sure to do so down-ticket as well.

Here's a question for everyone. What has his candidacy done in terms of the candidates that are getting their nominations down-ticket? Is his candidacy pushing the state and local noms to the left by motivating the more social oriented members of the party out and voting in primaries? I think he's going to go to the end because I personally imagine that he's pushing the nominated down-ticket candidates towards his view of what should be done, and he'll want to run that all the way to the last primary... because if he wants to see the kind of legislation placed on the President's desk it's important to affect the kind of legislator that gets elected.