Nukes are off the table, there is no world in which we will see another nuclear weapon used in war, if there are even any still viable nuclear weapons left. (Nukes degrade and cannot be effectively maintained, they have to be replaced entirely after a certain point, and officially we're past the point for most nuclear arms produced for them to be viable.)
But not only that, but no country on Earth would allow Israel or the US to live if they nuked Iran. Their propaganda has objectively failed. Over half of people (pretty much every single human under 40) in western nations do not support Israel in the Israel v Iran conflict. When you poll other countries, it drops to under 10% supporting Israel, with most countries not peaking past 1% support for Israel versus Iran.
China has the capability to unilaterally end the US economy entirely. They haven't because they have repeatedly stated they do not want to engage in economic warfare. If the US nukes Iran, the US economy ends. It won't recover. We do not have the raw materials or talent for it to recover. We have no other manufacturing base which can replace our current dependence on China. Add in the rest of BRICS, the fact Mexico is currently learning more towards BRICS than USMCA, Add in the fact no European government besides the UK supports Israel, add in the fact Canada is much more willing to work with China than the US right now, and there isn't a future for the US or Israel.
The US has lost the Iran war, past tense. The US Navy lost its first naval war. The US has proven to be an actual paper tiger, and without the US defending it, Israel cannot defend itself. Saudi Arabia is finding this out currently, as they are losing their genocidal war in Yemen against the rightful government of Yemen. The US promised to protect them too, and they can't. The US doesn't have the munitions to wage war, much less aid others wars.
I agree with you that nuclear is the last option they have left, it is the only way they can continue the war in any way that isn't a direct surrender, but I do not believe the people actually capable of launching a nuclear attack want to die and see their loved ones die for Israel. They will, explicitly, refuse to follow orders, regardless of how insane the people at the top are.
We currently have US military members refusing to follow Trump's orders. Why do you think Trump ordering them to kill themselves would be followed?