The balance of power in the Senate now hangs on the health of South Dakota Senator Tim Johnson, who would almost certainly be replaced by a Republican if he should become unable to serve.
Interestingly, South Dakota law only allows Johnson to be replaced if he actually dies. As long as he's alive it doesn't matter that he can't perform his duties. The presumption is that he will recover eventually, so he can't be replaced. Which makes me wonder: if Johnson were in a persistent vegitative state, would the Republicans be as eager to insist that he be kept alive as they were in the case of Terry Schiavo?
Not that I hope we ever get a chance to actually do that experiment. I'm pretty sure I know what the outcome would be.