Unintended consequences?
A short intense war would give China an excuse got kick up some dust.
Where else are the major powers going to get into it? The only other places it seems to make any sense would be Africa. We could go to blows there and not really wreck anything.
If we wreck South Korea, we make reunification possible. China and the US get to win for their economies. Russia can get in on it as well. North Korea is already a dump; and Japan would not be upset with a South Korean economic disaster.
Lets see, The US, China and Russia win. Japan wins. The Korea’s lose. Sounds fair to me.
Unintended consequences?
The thing with unintended consequences you do not know before hand what they will be (otherwise they would not be unintended).
I have no idea what the consequences be if we took out North Korea.
I do know that whatever President Trump does about North Korea, the left will twist it to use against him.