If we go to war with North Korea, China wouldn't dare cross us - they might complain a bit, but their military would stay away from us. NK is already looked down upon by nearly the whole world for their pro-nuke policy. While I don't believe they currently posess an actual nuke, there is no questioning that they have the materials to build it once they finish testing of the explosives. I really don't believe that NK will ever give up it's desire to attain nuclear status under the current regime. Not if we give them a non-agression pact and all the economic aid in the world. Unlike Iran, however, there is not a lot of resistance to work with in NK. I imagine that if the people collectively felt they could do better with a different government, it could happen, but that doesn't seem likely.
In the end, I think military force will be necessary to end the threat that North Korea poses. Better to do it before they get the actual nukes and decide to use them or give them to someone who will.