The Dems will not do so for political reasons. Their FEAR is that they lose more seats and will be in a worse position in the debate a year from now, so they choose to fight while they still retain power in the Senate.
The Senate seats up for grabs next year favor the GOP gaining Senate Seats because of the States on the list, and they know this. So they fight now while they still have some power in Congress.
That was prior to 1Oct13. As of now, every GOP seat will be up for grabs. This is going to backfire on the GOP and you wingnuts in ways you cannot even concieve of at present.