If NK had the ability to split from SK during a war that the US was in, i think it that they would be a little bit more of an issue than a little girl.
Except they were backed by China. We also have an army that is so much more incredibly advanced than there's. It's like if something from space were to attack us.
China is the only real threat in this, though I'm not sure about Russia. China will only intervene if we attack first, at least that's the impression I'm getting. Right now North Korea is like the 50's-60's Soviet Union, except they don't have any of the resources to keep their army working. The fact they can barely keep anything running now means if we were to attack there are no chances for them to even feed soldiers, which are less malnourished than the average North Korean.
If North Korea were to attack somebody, we would steam roll them. I imagine China and the US would have a few heated words about what we're doing. But if China and the US were to go to war, everybody would lose.