It's not clear there is anything Israel could do which would elicit more than strong, but carefully chosen, words of condemnation from the west.
Certainly Nuclear strikes against Iran would be a huge overreach. But no other country is going to retaliate with a Nuclear strike on Israel. If for no other reason than it would certainly lead the US deploying its nuclear arsenal. Especially with the current administration, no one would count on them choosing a path of de-escalation.
Other than strong condemnation, there would be zero consequences and no effect on west's support to Israel, if Israel would to use nuclear weapons on Iran.
Zero chance that the USA would abandon them in this scenario. We couldn't even get a Democratic President to even stop funding them during a genocide. We watched the "left" cable news station get rid of their most progressive voice for speaking out against it, in the same way they did back in the Iraq war days.
There is from the rest of the world. Israel needs the west on its side. Using nukes would guarantee that support would end, which would make them extremely vulnerable.