The fate of a nation and its people can never be determined by others, that too, by USA, which is thousands of miles away. North Korean Govt will not collapse, and it is not a federation of 50 states to collapse. It is a homogeneous country, all people united. Its people are united, disciplined and law-abiding. They are not gangsters.
China and Russia will never let it fall. On the contrary, there is every possibility that South Korea will go the South Vietnam way.