The worst part is that China will turn into a Super-Mexico and flood the world with illiterate illegal aliens. It'll be The Camp of the Saints time.
You are correct in saying that the collapse of American economy will bring down the Chinese economy, and ironically her ambition to become the World hegemon, replacing America. I always thought that the surest way to check Chinese aggression is for American economy to tank for a while. Not that I like the consequence of it in America. But my feeling was that American business and political community will continue to suck it up for China, blinded by the billion men market, without such an event.
I do see that any serious economic downturn in America this time around is something you cannot get out of easily. I do not enjoy this event unfolding. But the potential is there. It should be reminded that the American economic downturn can be triggered by an external event, such as the collapse of Japanese economy. Chinese economy may collapse on its own, too. There are at least three large economies wobbling at the edge of a financial disaster. Whichever falls first will take all the blame (for a while at least) and the rest of dominos will fall. At the beginning of 90's, the world looked so peaceful and full of hope. Things got seriously screwed up in a dozen years.