I disagree with your theory that Shas and Israel Beitenu will be reliable coalition partners for Olmert. They are both sectarian parties that can be easily bought, but they will bolt at the first sign of trouble, and their supporters are very right-wing (which makes their success so unfortunate, since I think their supporters will find their votes to have been wasted).
Maybe, although I doubt it, but then if that is true, the left coaltion needs only two Arab votes to carry the day. They will get them, easily. There is a decisive majority for unilateral withdrawal. It will happen.