As much as I despise McCaskill, I believe she would have beaten Akin even without that gaffe (though it would have been closer - probably a 6- to 8-point win or so). People forget that this guy ran a terrible campaign even before the gaffe happened, and there's a reson why Akin was her preferred candidate from the very beginning. Also, no Democratic incumbent was really going to lose in 2012 anyway, except MAYBE Nelson in NE. Honestly, 2012 was an absolute disaster for Republicans at all levels.
McCaskill absolutely would have lost, even his weak campaign would have been enough to cost had it not been for the gaffe, his money absolutely dried up afterwards. He was leading, and beginning to pull away in some polls. In fact the only reason mccaskill won by so much is all the undecideds broke for her at the end.