If ever no one is buying Bitcoin anymore the price value will be drop for sure,it rely to people uses Bitcoin if there is low of demand and high of stock the price value will decrease,if it will continue to this case it will last into less value.For now it is impossible to happen because people already know how important bitcoin is,and it is also a way of long term investment.
There wont be any chance of this in the future because the governments of different countries are seriously talking about legalizing the crypto currency so that they can provide some alternative solution to the people.
Mexico has already passed the bill in the lower house and Thailand is also very serious to pass it so that the people from different countries who visit Thailand as tourists can be increased. In the worst ever condition, if it happens, then just hold whatever you have in your wallet and wait for the right time to sell.