I suppose the nuclear fallout would depend on how the wind blows in that part of the Middle East. Obviously, there would be retaliation, but Israel would have wanted to strike with nuclear weapons before the other countries would have that capability. Once Iran has nukes, they'd be more likely to strike Israel in reality (not just in fantasy, as in my thought experiment of imagining what the world would be like if Israel were as evil as most Muslims there believe). Mind you, the US would then annihilate Iran, so it would be suicide.