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.
sourceYour asking about the possibilities of Bitcoin falling to zero but your Poll seems too different from the title.
And also you have already answered all the possible questions.
For me, bitcoin will never fall to Zero because what ever happens there are already millions of Bitcoin that in the air and that means BTC will have a permanent value .
and about the Poll? I will Sell if the price fell down to 40k and will wait till the value drops to 5k and Buy all my funds and then rest to the grave .