But those short term attacks are not the real problem from the Israeli perspective. The real problem is that anything that helps get rid of Assad is very likely to be bad for Israel.
Israel probably realizes that they're better off with Assad than with the rebels just as Israel better off with the Mubarak's Egypt and the newest Egypt than with Mursi's Egypt. Better a hostile but sane neighbor than a hostile neighbor convinced that Allah is calling for genocide.
Assad is afraid enough of Israel to limit the support he provides to Hizballah. If the Syrian rebels win and if the extremists have any influence--which they seem to have-- we can expect to see the limits on what sort of weapons go to Syria, including WMDs, quickly, even if only temporarily lifted. And if you believe that the UN or any other organization can be sure it gets all of Syria's chemical weapons, where a man can carry enough to kill thousands, then I've got a great deal on a time share for an over water transportation system in Brooklyn I'd like to interest you in.
Syria transferring advanced Russian weapons or residual Syrian chemical weapons to Hizballah is the real nightmare for Israel. Hizballah armed with long range missiles loaded with nerve agents that can be absorbed through the skin, and hence not stopped by gas masks, could be an existential threat to both Israel and the Middle East.
It's not inconceivable that if thousands of Israeli citizens are murdered by a Hizballah chemical attack that Israel will retaliate against Hizballah, or Iran, with nuclear weapons. Before rejecting that possibility ask yourself what the American public would demand if Hizballah killed hundreds of thousands of New Yorkers with a chemical attack?