there are already 18,600,300 bitcoins mined. also there is plenty of miners outside of china, probably about 50%.

so the only thing that will change if china stopped all bitcoin mining is that blocks will take about 20 minutes, instead of 10 minutes. for two weeks.

this wont have much effect on price at all, if anything it could make the price go up since presumably all the bitcoins in china would be inaccessible for a while.

if it is some sort of permanent loss of 50% of mining power and 50% loss of all bitcoins, that would double the value of each bitcoin!