It's simple. If Iran acquire nukes you'll have a choice:
1) End hostilities and try to save situation diplomatically, like, through some kind of deterrence game and building new system of collective safety of Middle East (with equal safety for everyone, including Persians, Jews and Arabs).
2) Fight and, highly likely, lose a limited Nuclear War in Middle East (because Russia, China and North Korea have much more tactical nukes they can give to Iran)
3) Escalate and fight a large scale nuclear war against Russia, China and North Korea simultaneously. I don't see how you can win such a war, but you are smart guys, I'm sure you can figure something out.
Yep. They are definitely more sane than Radical Chabad or some Radical Evangelical "Christians".
Technically, Russia can leave Middle East, but even then Russia will leave scorched land behind. But much more likely, that Russia will escalate.