I’m not so sure about the details of your scenario, but I’m in general agreement with your idea that Iran is much more likely to attack through surrogates than to ever launch a first strike from its own territory. In fact, Iran will go to great lengths to make it look like a terrorist nuke originated from anywhere but Iran. This makes a nuclear Iran more dangerous than any other nuclear state, because the deterrent effect of the idea of mutually assured destruction only works when you know who the perps are. Everyone knows this, that’s why even the Europeans are starting to make some noise that it’s a really bad thing for Iran to get nukes.
It is laughable. The Europeans couldn't find their own backsides with both hands. They couldn't agree to mention Iran by name in a joint press release expressing concern, as recently as two weeks ago. Europe isn't going to do a damn thing. Some of them know this is hopelessly irresponsible and are concerned enough to bleat about it a little, purely for blame-diversion purposes. They might agree to cancel a couple of visas or restrict a checking account. But act, with force sufficient to break the Iranian regime or their physical capabilities? Not a chance in hell.
I had dinner in London with a British security type in 2005, right after the tube bombings. We talked about Iran. He said Iran wouldn't get nukes because it would be bad, therefore it would not be allowed to happen, but Americans were going about it all wrong. He thought the problem was to buy them off in a way that kept possibilities of trade open to make money on their oil. Just hopeless. I told him point-blank that Iran was going to get nuclear weapons and the world would watch and do nothing. On the news, after three minutes detailing police efforts to catch those responsible for the attacks, the BBC was wall to wall mullahs lecturing the British for being racist bigots - on the day the buses were being bombed. I swear I am not making this up.
I was right then and I'm right now. I don't like it, but there it is. If Bush with all our firepower and on an active war footing did nothing about it for six years, Obama isn't going to do jack squat. And the Iranians know it.