The same problem exists now as before, we irradiate Moscow, they irradiate us. They still have nukes too. But you forget the threat of Western sanctions will require retaliation. All the hawks calling for blood had better think twice before continuing this America is the policeman of the world crap. Keeping in mind part of the 17 trillion deficit can be directly billed to that idea, economic collapse is just as big, if not a bigger threat, as any war.
If they hand nukes over to Iran, they are nuking us by proxy. That would be like us handing nukes to Chechen terrorists. If that's what they end up doing, that's just Russians being Russians - burning down the world so they can realize their dream of universal empire under Russian rule. Plus ça change, plus c'est la même chose.