I believe that Israel has enough nukes to destroy Iran. Bibi's problem is that he has said that Iran presents an existential threat. If that's true, then he has no choice but to use every weapon in his arsenal to destroy Iran. Of course, if he doesn't believe that Iran presents an existential threat, then he won't. Who knows what he really thinks? Has he painted himself into a corner? If he does nothing, how will history judge him and his statements?
Again I think you're right though, if Israel's back is to the wall, they'll use anything and everything they have. The {expletives} in Tehran and elsewhere would do well to remember that. It's one thing to bluster about "wiping Israel off the map" etc. but it is another to realize that in order to actually do that, you are going to absorb a dozen or so nuclear weapons. I realize the muslim fanatics are not entirely rational by our standards but... The idea of the heart of your nation getting cut out, millions dead, hundreds of square miles of radioactive wasteland... That's got to give you pause. I hope, but I'm not counting on it.