Have to toss divided states I think. Not sure how many states have 1 Senator of each party, but I understand a state delegation tie results in a null vote.
8 states are currently split 1 each pub/dem, 2 states (Maine and NH) are split 1 each independent/dem (assume independents will vote democrat), 22 states have 2 pub senators, and 18 States have 2 dem senators so that would likely end up at 22-20 for pubs.... though Romney would likely split his state so you end up with 21-20 provided no other defectors.