I feel more confident every day that the country to roll on North Korea will be China.

We don't have the willpower, South Korea won't risk the wholesale destruction of their capital, and China's interests in long term stability and trade practically compel them to move. Rush in, disassemble the ruling hierarchy, install a puppet government to keep everything running, and the American/South Korean military off their doorstep. They'll wait as long as they can, trying to help the North Koreans get everything together, before everything goes down.

China will bide its time until the right moment, then everything unravels practically overnight.