While understanding why Israelis might justifiably be nervous about the new government in Cairo, I've always been dubious that Egypt actually was going to repudiate its peace treaty with Israel. First, the minds of most Egyptians are primarily on other things right now. Second, one generally doesn't repudiate a peace treaty unless one is willing to go to war (otherwise, what's the point?), and I don't think the Egyptian people are in any mood for an actual full-blown armed conflict, nor do I imagine the Egyptian military is currently prepared to engage in such hostilities even if the populace were. Finally, and not insignificantly, there is massive international pressure against Egypt repudiating its peace agreement with Israel -- meaning that the Egyptian government won't take that step without some very strong reason (be it irresistible domestic pressure or provocation or what have you).
But one always can worry (and I do think it is notable that, reputation for rabid warmongering aside, there is no political constituency of note in Israel that has called for a repudiation of peace with Egypt. It seems that once Israel makes a final agreement with one of its neighbors, it is capable of keeping it with little fuss from its citizens' end). So I was gratified to find out that the planned "million man march" in Cairo calling for an end to peace with Israel apparently only attracted a few bare hundreds. This doesn't surprise me -- while I imagine the Egyptian street is probably rather cool towards Israel, I also, to reiterate, think they're mostly concerned about other issues right now, and are not keen on reverting back to old patterns where mad gesticulations towards Israel are used to distract them from necessary reforms at home. There, now, that playbook isn't going to fly.