I don't think this is going to happen, even if Palin at Thursday night's debate proves herself to be even less prepared than what she revealed in the Gibson and Couric interviews. McCain, I believe, will have to grin and bear it and ride out the wave until November 4, because removing Palin from the ticket would devastate the base and completely ruin the Republican chances. It could also hurt with downballot races, as Nate Silver points out here (among other things) in a great post on this subject.
But, who knows, maybe it will actually happen. It would certainly be the icing on the cake to the farce the McCain campaign has become.