If China banned ASIC production it would hence be more profitable for other jurisdictions to enter the competition for the supply would be lowered with demand staying the same.
On the issue of Quantum hacks there is two things that we must keep in mind. First, Quantum computing has not yet been developed for this purpose and isn't projected to reach this level within the decade. With this, the Bitcoin industry is one of the most innovative and when people who are Satoshi trillionaires are threatened with having their wealth evaporated, it will be in their best interest to innovate around this potential risk. Secondly, any attack on bitcoin that proved to be massively successful would likely kill the network entirely. Those who stole would end up with nothing of value.