If there is no demand then the price will go to 0$ but as mentioned above, that's unrealistic and impossible to happen.
Yeah! Of course if one person doesn't buy bitcoin, it doesn't affect to the price either dump or pump. When a person do a lot of bitcoin then he sell for too cheap, the price must go cheaper and if he holds the bitcoin it has a big chance that the price must be more expensive when there are more demand.
We can say that anything you do regarding bitcoin, it can take some result on it's price. We also do a thing that can cause bitcoin for dying.