Less miners = More Demand = increasing price, as simple as that.
but isn't that will make bitcoin become centralized?
because the number of people who help run nodes for mining is decreases
AFAIK miner china is the biggest hashrate holder on the bitcoin network
Please take a look at the latest bitcoin node distribution around the world and china is not holding the majority of nodes.
https://bitnodes.earn.com/that will enough to answer your question about what will happen if china bans miners but these miners already speculated it and they can move their operations of bitcoin mining to avoid the regulation that issued by china's government into another country.