Of all the nuclear scenarios, a strike by Iran presents Israel with the "cleanest" options. Iran is a nation-state and has targets of value as well.

Israel could not simply stand down -- politically unacceptable -- but Iran has a number of primarily military site that could be targeted in a counterstrike producing fewer civilian casualties than would any strike in Israel. For example, the Iranian naval drydocks for their diesel sub fleet would likely not last long. Thus, Israel could counterstrike as would be a political necessity, but could do so at a "counter-force" target and avoid the approbation of a "counter-value" strike.


Of course, the most likely scenario for an Iranian nuclear strike on Israel would be a truck or cargo container driven into Tel Aviv (comparatively little arab/palestinian presence but lots of Israelis) by a jihadi from one of the militant sects available. Even if the nuclear signature were linked to an Iranian facility, Iran would claim that the material/device had been stolen (actually, this could even be true given the odd relationship between Rev Guard and formal military/security organs), that they had not notified anyone for fear of embarrassment, and that they had no responsibility for the heinous act. Israel would be unlikely to attack the terrorist base responsible for the direct attack, as it would be sited in a major urban area just chock full of innnocents, and would be viewed as a nuclear agressor if they struck at Iran after Iran had said they weren't responsible and apologized for their poor internal security.

Most likely result would be no counterstrike. This lack of response would be followed by a rapid vote of no confidence, ushering in a new and decidely conservative/hard-line governing coalition. The inevitable crackdowns in the territories would generate increased "hero" status for Hamas, Hezbollah, and whatever other group (if any) pulled off the physical attack. Since this
would increase recruiting and polarize the situation further -- both of which would enhance the power of these non-state actors -- it is very much to their benefit to carry out such a strike as soon as they can procure the materials. For them, it is win-win.