Zero! That is extremely wishful thinking. Even as a historical artefact Bitcoin will never go to $0. Hell, Bitconnect is still trading at $0.69 with $13,000 volume today. I really hope this is wash trading.
Bitcoin will be a multi-decade artifact at minimum. A novel collectable.
No fiat currency will go to zero.
Not 0 due to the cost of printing, but 4.2 trillion Marks to $1 USD in Weimar Germany 1923 is pretty close. Given that they aren’t in circulation now, I think we can assume at least some period of 0.