If there is no demand then the price will go to 0$ but as mentioned above, that's unrealistic and impossible to happen.
True. If no one will be interested into buying bitcoin anymore, then the value will gradually drop until it reaches $0. All bitcoin everyone acquired in their wallets will be as good as stone - nice to have worthless cluttering stones. But as mentioned, it is unlikely to happen because what are the odds that each and everyone will suddenly decide not to use bitcoin anymore, right?