(because that is what I would do)
The Chinese are faced with an interesting strategic decision. They can occupy North Korea if they're willing first to fight for it and then to repair it. What that gives them, though, is a direct border with South Korea without the buffer state that North Korea has been for half a century. Alternatively, they can allow the South to reclaim the North after the latter's government goes down. The advantage to China is the immediate and enormous cost to the South of reunification. According to a story on FR this evening, that was and continues to be a crippling cost to Germany under similar circumstances. Two trillion Euros. The mind boggles. But in a few decades Korea will be improving and then they'll have that 879-mile border with a presumably hostile state all over again.
Chinese planners are notorious for the long view, and so I don't think that will be all that attractive an alternative. Their preference must be for a continuation of the status quo, which is a client/satellite/buffer state in the North with a government less pathological than the present one. If I were betting on the Chinese strategic objectives here, that would be where I'd place my money.
There are problems even with that, naturally. That government must be established and maintained and the country fed by China. From a cost/benefit analysis, the longer they can delay action, the better from their point of view.