The most likely red state Senator to survive is Heitkamp IMO. Tester makes it somewhat close. The other three (especially McCaskill) will need a miracle to survive if Clinton is president.
McCaskill is probably toast regardless. She's just given her opponents too many videotaped extreme statements and gaffes. Unless another scumbag like Akin gets nominated, of course.
In order to survive, these other red-staters need to continuously vote against their party line from time to time, not just try to do it when the election is near. Tester, Heitkamp, and Donnelly have done OK at this, and Manchin has done well. All could survive, but all will of course have to deal with the unpopularity of their party locally.