1. Will Bitcoin ever fall to zero someday?
Give a proper argument why bitcoin will fall to zero? until now I don't see one strong reason why bitcoin will be at zero, regardless of how the government tries to spread negative things about bitcoin and what I understand from your post, it has to do with government policies that will prohibit the growth of bitcoin globally and is this the only stronger reason to say bitcoin is going back to zero?
But realistically that also doesn't happen and many governments actually allow legal bitcoin as a commodity asset that can be traded and even El Salvador has legalized bitcoin as a legal transaction tool. Therefore the chance for bitcoin to be zero is completely impossible because of the strong assumption that the government also does not do that. There are several countries that have banned bitcoin completely, both as a commodity asset and as a legal means of transaction, but so far this has not affected bitcoin in any way.
2. What happens if it ever falls to zero?
When zero assumptions are impossible then what will happen we will never know, even people's belief in bitcoin will return to zero is not the same as altcoins and shitcoins which on their journey are pumped, dumped and die.
The point is not that bitcoin will or will not fall to zero, but that the blockchain will continue to work well anyway. Although zero is impossible because the measure of value will still be there, bitcoin can still be used to buy or sell goods. If the dollar becomes weak, bitcoin will be measured in another currency.