Given the choice of having the worlds fastest growing economy at complete arms length versus having them involved to the extent where they need the US economy not to fail and I think I would take the latter.
In the past 10 years the percentage of China-US exports has dropped from 50% to 25%. If that continues at this rate China will not be dependent on exports to the US anymore in a few years. http://www.uschina.org/statistics/tradetable.html
Moreover the cost of stabilizing the US economy is rapidly increasing. China exports around $300 billion to the US yearly. But they already sinking over $150 billion annually in the treasury hole. If the budget deficit of the US will grow without a corresponding economic (consumption) growth, then you will end up in a situation where "investing" in the US no longer makes economic sense.
And then it is just a matter of reaping the technology, raw materials, food and cheap labour. And in that case the harder the economy fails the better. Remember, for the Chinese, the fall of Russia (also once a respected trade partner) was one big garage sale. Same for the Asean crisis and the south american currency crisis. So far every crisis has allowed China to come out unscaved and even better. When US credit runs out, I think you will have a hard time convincing them not to drop the US.