If by chance that there will be no one stop buying bitcoin then it will be totally not usable and no more value than what it was, because bitcoins value or price really determines the demand of the users who owns it. I don't think that it will happen right now and I don't think also that it will be because is the digital gold to be exact on this century in fact if you just hold or reserved it that would be a good asset because the future will lies in to a digital world.