Since the death of Kim Il Sung in 1994, the U.S. and South Korean governments have gamed scenarios for the collapse of the North, with the triggering event usually posited as the death of Kim Jong Il.
While Kim did not spend decades grooming his heir the way he was prepared for leadership, he did leave in place a governing structure to protect his family. The generals and party leadership have every incentive to support Kim Jong Un as the "Great Successor," and his uncle, Jang Song Taek, as the power behind the throne: Their own survival depends on a successful transition. In the coming months, the most likely scenario is not instability but national mourning and a retreat from recent diplomatic interaction with the United States and South Korea.
By the middle of next year, however, fissures may be apparent within the regime. Commentators frequently explain North Korean nuclear and missile tests as demonstrations of pique or efforts to gain concessions. That is true in the tactical sense of when exactly Pyongyang chooses overt demonstrations of its weapons development. It is not true, however, in a strategic sense: The North Koreans have a long-term program for developing nuclear weapons and using that power to make demands of the United States as an equal nuclear weapons state. The propaganda machine long ago marked 2012, the 100th anniversary of Kim Il Sung's birth, as the year the North achieves that status.