Concurring with Ezra Klein and Kevin Drum, I'm reasonably confident that Sarah Palin will cease to be a player in national politics after the McCain/Palin ticket goes down in ignoble defeat. Sure, the base loves her. But, as Klein notes, Gov. Bobby Jindal (R-LA) inspires the same sort of love while still managing to be coherent (indeed, quite articulate) on matters of national policy. Republicans are not utterly insane -- they know that Palin has become synonymous with all that the American center (much less the left) finds detestable in the current GOP. There is simply no way any reasonable Republican will decide to double down on the biggest failed bet of the 2008 cycle.
I'll just add that in the first set of 2012 Presidential GOP primary polls, we'll inevitably see Gov. Palin's name high on the list. This is solely a function of name recognition -- remember how well Joe Lieberman was doing early in the 2004 cycle? Let the primary season swing into full bloom, with some genuine solid Republican candidates running against her, and she'll be taken down right quick.