If, say, Iran hit them with a nuclear device and they are crippled but hurl a country-destroying salvo back at Iran and beat back attacks from Lebanon and Gaza do they still have deterrent against advancing armies from Syria and Egypt in a scenario that lasts for days or weeks?
It wouldn’t take 400 nuclear weapons to destroy the bulk of Iran. There would still be enough left over to take on other enemies, I would think. Building an atom bomb is one thing, delivering it is another. It will probably be awhile before Iran is able to fit a nuclear warhead on to a missile unless someone is helping them (the Russians? AQ Khan?)
By now, the Israelis might have thermonuclear weapons (”H-bombs”) which is a whole different ballgame. The trigger for an H-bomb is an A-bomb, IIRC.
That’s where God comes in.
If Iran hits them with a nuke, no one is going to invade. It’s like signing your own death warrant. Israel is not that big. Ironically, the West Bank and Jordan would be looking at serious radiation problems.