North Korea's missiles are not noted for their accuracy , so there would be a real danger that the missile would land on Guam. It would could be the best case scenario for the States, as China would have to up its game against North Korea, and take more serious steps then simply limiting trade. Nations that are on the fence with respect to supporting the States, would have no choice but to line up in support. Kim would lose any bargaining power as he would have crossed the line and inadvertently attacked the States. Depending on where the missile landed , there might be no loss of life, but again accuracy is debatable, so any loss of life would demand a strong response from the States.In an analysis of various scenarios Kim might well have determined that any error with the missile launch would pretty much spell the end of him. It is often the case the dictators are removed from power and life on miscalculations as Kim must be all too  aware of.