* How would the US respond? * How would countries like China and Russia respond in turn? * Would it be the beginning of World War III?
The linked article is what prompted these questions.
Complete destruction of North Korea, which is why they'll never do it. Sadly Mutually Assured Destruction is the best deterrent to the use of nuclear weapons. This is also why terrorist organizations scare countries so much, it is hard to reciprocate when there isn't a clear actor.