It would be nice if it were that simple.
What other options would North Korea have, if China pulled the plug on their continuing support for their regime? Here is a list of Global Military Strength Rankings.
Global Firepower Military Ranks - 2013
The USA is ranked #1, China #3, South Korea #8.
In contrast North Korea is ranked #28. Could North Korea take on China militarily? I don't think so. And if one factors in their belligerent relations with the USA and South Korea, the situation looks even grimmer for them.
It is also unfortunate that the North Korean people (due to the sanctions) are not getting a chance to benefit from the economic growth that China is benefiting from.
I take it you or others believe that the North Korean elite would prefer to incur a military defeat than to bow to the reality of their situation?