If he does win, will that drag down the entire party in 2014 or 2016?
One poorly spoken candidate in a statewide race will not have implications that large.
I still think Akin has an even or higher chance of winning. Many Republican voters in his state will not abandon him just because of one comment. And don't forget he's up with independents. Does anyone actually think the NRSC or outside groups will actually abandon him unless he's down by more than five points? I don't think so. McCaskill is still very beatable, but this has not made her a lock, shoo-in, or even favorite, as some seem to think.
No predicting what happens if he leaves the race though. A lot will depend on the rollout, candidate quality, McCaskill's response, and media coverage.