What will really tank card prices is if the miners in China decide to dump all their now useless graphics cards and get real jobs. They could drive prices down below MSRP on eBay easy. Should be fun after years of waiting to get a card at a reasonable price.
I think this is where you are mistaken. The bulk of the graphic cards are soaked up by people that can afford to run massive crypto mining farms. In other words, they are well to do in the first place. The small time miners affects GPU supply, but their contribution to the problem is just the tip of the iceberg. In this case, it is the closure of these massive mining operations that made a huge impact to the supply. But as to how long this will last, it is hard to tell. While they cannot mine in China, it does not stop them moving to other countries to continue their mining activities. There is a lag time before they relocate. Big mining operations have the economies of scale to continue mining even if the prices are low, and with current Ether prices and lower difficulties, it is even more attractive for them to continue.