Sounds like the Likud rank & file is leaning away from the "disengagement" plan. On the radio this morning Roni Milo (former MK who rejoined Likud after cofunding a defunct centrist party) was making predictions of economic chaos if the plan is rejected. That's a sign of desperation on Milo's part.

If the plan is defeated then the Likud would be likely replace Sharon somehow (though Sharon has not said that he would resign). Netanyahu seems to played his cards pretty well recently by exhibiting lukewarm pseudo-tough-guy support for the disengagement.

A lot of people think that once the Likud has "voluntarily" accepted the plan, the US will be free to gradually water down its statements regarding Palestinian refugee campees and borders (eg. this very Haaretz-y article which mentions that European leaders have been uttering the words "right of return" a fair amount lately, incidentally demonstrating that siding with the Palestinians is the only guiding principle of their policies).