What if another Korean War happens to occur?

What if another Korean War happens to occur?

Personally I want peaceful and gradual unification of Korea.
What if China fails to control North Korea and North Korea continues to increase tensions between America?
China can still stand behind North Korea even if North Korea attacks America?
How long can China play the role of North Korea's close friend?

It seems obvious that North Korea has nuclear weapons.
The military power of USA is much better than that of North Korea, but if the USA fails to destroy all the nuclear weapons at the same time, North Korea might have a chance to revenge the mainland of the USA with nuclear weapons. This will be a disaster, but both China and North Korea will pay the price for this. I wonder if Kim Jong Un is such a stupid person.

I hope North Korea will sit for the peace talk unless they can survive from all the financial sanctions opposed on them.

http://www.alt-market.com/articles/3254-korean-war-part-ii-why-its-probably-going-to-happen

Another Korean War will be the worst choice South Korea and the USA can make.
Is it impossible for Korea to be united in the peaceful and gradual way?