The real question is how much has Kim's opinions changed since he got back to North Korea. I don't think he's foolish enough to launch an attack on South Korea, Japan, or the USA. And if they do, it'll probably fail. Just look at North Korea's missile launch attempts...but if it does succeed, they better make it count, because the USA will peel North Korea like a fucking orange. It'll make the immobilization of Libya look like child's play.
And that's assuming that North Korea doesn't get a nuclear response. I don't think Obama would allow a high-yield nuclear warhead to be released, but I could see bunker busters being dropped on North Korea's nuclear facilities.