Its probably not very likely that if a large buyer pulled out, NVIDIA could just sell to other customers. If a large buyer pulls out, that's a massive signal to everyone else to begin cutting costs as well. The large buyer either knows something everyone else doesn't, or knows something that everyone else has already figured out. Either way, the large buyer pulling out signals "I don't think the overall market is large enough to support this amount of compute at these prices at current interest rates" and everybody is doing the same math too.