They can easily be sold once they become unprofitable.When a card is bought, most people modify bios, undervolt and overclock it. So they get even more computing power and less power consumption.Also you get for gpus 1,2,3 years of waranty.
II like your thoughts about people like Vitalik. Indeed, from this point of view, what will happen to the currency if the creator gets into trouble with the authorities.