If the US will not come to the aid of Israel in a nuclear war crisis with Iran, then Israel will have to use whatever assets they have at their disposal.
No nation would accept defeat & annihilation as long as they have weapons to defend themselves & to retaliate against an attack.
That could very well be nuclear weapons.
I suspect the next use of nukes will be the start of WWIII, as the nuclear fallout will spread in all directions, killing thousands to millions of people in the area. Russia borders Iran, as does Pakistan. Both have nukes & both would be royally PO’ed to be the victim of Israeli nukes. China is not much farther down wind.
I think Russia, Putin in particular, would go ballistic - literally. The fallout from Russian thermonuclear weapons would then spread to NATO countries & around the world, bringing other countries into the war. American citizens & military would be caught in the line of fire & die in droves.
And there you have it: Worldwide thermonuclear war. The supposedly civilized world could end in a matter of days & there is no one who could stop it.
Once the first mushroom cloud appears, those with nukes will want to launch quickly against their enemies as preemptive attack is the only possible way for one’s country to possibly survive. If Putin attacks Israel with nukes, he will probably attack the US as well as he cannot be sure the US would not come to Israel’s aid.
The only sure way to avoid this scenario is to stop the aggressor Iran before it has nuclear weapons & the means to deliver them to Israel.