China's collapse would be a complete and utter shitstorm. The loss of the world's second largest economy would have a huge ripple effect. The US and other nations may bitch and moan about China's policies but they wouldn't let it collapse. There would need to be some kind of revolutionary group they could support ([i]*cough* Afghanistan *cough*[/i]) to place in power, but given China's current stance on those who deviate from the party line, that'd be near impossible without open war.