China is a very different, and very complicated situation, but they are currently enjoying more political influence than at any time in recent history, and as they are poised to become a dominant world power, North Korea is a liability that they may well decide that they cannot afford.

I would also point out that our respective notions of "live on" must be a bit different; assuming that the data I've read can be trusted, North Korea has almost no paved roads at all [1], which means that the movement of supplies throughout the country is badly hindered. Given the well-known height differences between North Koreans and their South Korean neighbors, the gulags and other oppressions mentioned in this article and others, the threats which North Korea uses to squeeze aid in the form of energy and other supplies from other nations, their nearly complete lack of electrical lighting after dark, and what's known of their trade with China, I find it difficult to see North Korea as being on anything more than the barest of life support from China.

[1]: http://www.tradingeconomics.com/north-korea/roads-paved-perc..., among others.