Well, actually, just *ONE* nuke anywhere in Israel makes most of the country uninhabitable. It's pretty much over at that point, for next 10000 years, give or take few months. At that point I think Israelis would devastate ME. Everyone'd get nuked. Keep in mind, in those places fallout casualties would be tremendeous. While I'm as of yet unlcear whether the Mullahs in Iran really have a deathwish (rhetoric notwithstanding), or they're just taking a page from North Korea's extortion handbook, Syrians, a secular Baathist regime, has absolutely *zero* interest in a such a scenario. Question remains whether Mullahs would sacrifice the entirety of their country to destroy Israel. I really doubt they are crazy. Everything so far points to a calculating regime.
THAT is why it will not be allowed to get off the ground. Somebody will preempt. The loss of life will still be tragic. But the loss of life in a nuclear world war will be a catastrope for the entire planet. Nuclear winter will follow. Humanity will perish.
The Imams of Iran naively believe they will survive and ride out the response. There will not be an Iran after the attempt to attack Israel.
IIRC, the U.S. set off some 90 nukes above ground in New Mexico and Nevada and there are people living there now. Not 10,000 years in the future.