If Kerry wins, all bets are off as far as the Senate staying Republican.
Odds are we still keep both houses of Congress, IMHO. The House looks like a lock for the foreseeable future because of gerrymandering.
The rats have to defend 19 seats versus 14 for the pubbies in the Senate with 5 open seats in the South, IIRC. It's possible that I may have to eat my words, but it doesn't look probable.
As long as the pubbies have one house you can have at least gridlock.