Minxin's case is built on the fact that no family dictatorship has ever succeeded into the third generation, and the circumstances in North Korea don't bode well for a precedent breaker here. Rising resentment, Kim basically begging abroad for money, and a military that has been starving for years do not inspire confidence that the regime will continue. Moreover, the complete failure of the attempted monetary reform shows that the security services that do exist will not squash a full-on riot.
The question then becomes how long will Kim hold out? His health has been going for years, and yet he is still alive. He's 70 years old, and has diabetes and has suffered at least one debilitating stroke. It cannot be too long until it happens; hopefully, the region will have a plan in place.
(One quibble with Minxin's piece: The US and South Korea are both taking this problem seriously, and have begun discussions about that very likelihood.)