If Israel has a nuke, they ought to use it. But then Russia would probably nuke them. We, i.e. the U.S. under Obama, sure isn’t going to do anything to stop this. Either way, this will not end well for Israel.
If the Jews weren’t so adverse to the effects of chemical/biological warfare, that would be a great way of depopulating Gaza. Pump the tunnels full of sarin/vx to kill terrorist scum, and shell in CS/non lethal irritant into the population areas....keep it up north to south until the population is in Egypt or the sea.