Here are some scenerios that can cause the price of btc to fall drastically. (In my opinion, it is highly unlikely and the possibility very slim).
(1) No way to trade bitcoin or exchange it for goods and services.
(2) All governments of the world placing a ban on bitcoin and bitcoin related activities making it highly illegal.
(3) The entire bitcoin network and nodes going offline making it impossible to even make underground transactions in bitcoin.
(4) Another crypto overtaking bitcoin and value and more people shifting investment to this new crypto.
sourceIs possible for bitcoin price to fall to zero and before such a thing happened that means people are no longer interested in anything concerning cryptocurrency, but bitcoin price can go down that does not mean that bitcoin price can go down to the scratch, many people from their own knowledge of understanding of bitcoin.