Those stocks will run out eventually. Huawei is probably betting on the sanctions being resolved through negotiations and the Chinese government making concessions on trade.
However, I wouldn't count on this happening since the U.S. knows very well the power of being able to spy on adversaries and allies using network and telecom equipment. I don't believe Trump will back down on Huwawei no matter what the Chinese government offers.
Apparently not enough as Huawei seems pretty nervous about it. If your competition is using 7nm and 5nm parts and you're stuck in the past with 14nm your market share will erode very quickly, especially in the smartphone business.
Mind you that other Chinese smartphone makers do not (as of yet) face the same restrictions and are able to purchase the newest parts. What chance does Huawei stand against them, even in the Chinese market? I'd say very little.
However, I wouldn't count on this happening since the U.S. knows very well the power of being able to spy on adversaries and allies using network and telecom equipment. I don't believe Trump will back down on Huwawei no matter what the Chinese government offers.