I'm extrapolating into the future.
If there were anything like a nuclear attack on a U.S. city, it would be for the oft-stated strategic purpose of creating the Islamic Caliphate.
That would be a physical place, populated and run by physical Islamists. That's their ultimate goal.
Such a state would be populated and governed by Islamists with a demonstrated capacity to use offensive nuclear weapons in the furtherance of their goals.
I do not believe that Russia, China, India, Israel or even the EU would allow such a state to exist or certainly to possess nuclear weapons for even a short period of time time. I believe (rememember, this is a scenario, not a prediction) that the world powers would consider any Islamist use of nuclear weapons to be an extreme, immediate, and intolerable threat to their own safety and security. Pakistan comes immediately to mind.