How do you figure? During GWI, Saddam launched dozens of Scuds at Israel & couldn't provoke a response. Granted that the US was telling Israel not to complicate things by retalliating. IIRC, Israel reserved the right to retalliate IF any of Saddam's Scuds were carring Gas, Biotoxins, or radiological warhead (crude A-Bomb).
Israel will probably ride-out any small-scale missile attack until they can tell if it involved WMD's -- at THAT point, the gloves are off. Up to that point it will be Tit-for-Tat, except that Israel will want to hit a little harder to prove that they can dominate any escallation.
Well, Saddam Hussein is dead, we pretty much own Iraq - that didn't work out well for Saddam.
Actually I heard from a military friend that we had to turn back Israeli fighters with nukes during GW1. I believe they have the stones and common sense to defend themselves if we aren’t there to take up the slack.