How would Chinese economic collapse affect dollar?

China supports the value of the dollar by buying US Treasury bonds. If China had an economic crash then they would likely sell off their Treasury holdings (2 trillion worth) to keep their economy going. This would flood the bond market with T-Bills and collapse the value of the dollar.

The government is creating so much money, borrowing so much, the dollar will collapse soon. This is why gold is up, it is a safe currency that cannot be devalued. It always retains its value, its nominal value merely fluctuates in relation to the value of paper/Fiat currencies.

Buy gold.