Of couse the Muslims wouldn't be so stupid to attack the most limited water resources,so that a single castle could hold them back.
And in this case the troops wouldn't time out easily, they would wait their time for the revenge. The only problem would indeed be water.

Further, I can't imagine the Crusader States not putting up a real effort to halt the invaders by arms. The martial tradition among these states and their warrior elites was enough to ensure they would take to the field. After all they did believe to a great extent that they were fighting for God.

So if the Muslims chose a more wet route the castles wouldn't have many chances, with their garrisons stripped and the Muslims not giving up. And there we have it, the determination, the strength and the better set up for sieges for the Muslims would in this case spell doom for the Crusader States.
Perhaps Acre would as in real history survive some time yet, perhaps a few other places, but the majority of the Levant would return to muslim rule.