Bitcoin technically can never go to zero. You can't get something for free, that is not "sale" that is "giving".
if nobody is willing to buy (at any price), i suppose the price is zero.
However it is also impossible for bitcoin to go down like that ever because I know that I will buy all the bitcoins in the world if that happens. I know there are a lot of people that feels like me.
you say that now, but that's because there is an overwhelming faith among so many people that BTC will succeed. what if that faith were shattered? what if the historical long term uptrend breaks down, and hash rate plummets? what if BTC's popularity/usage ends up following a trajectory like early dotcom companies?