I would be so happy because if the price of BTC is going to be zero I can then buy a million of the coin without using money. Well, jokingly aside, I think you mean what if one day BTC is going to be worthless or just forgotten by the people and is wiped out from the face of the Earth. So what if this will happen? I think the first question is: Will this happen? And I don't think so...that is already impossible.
Yes bitcoin can only get to zero only when it is worthless or many people do not have it in there possession this can only be possible when we have a new cryptocurrency that betters bitcoin or a hard fork of bitcoin and everyone is expected to move to another network and those still holding bitcoin will then have it to be worthless, now the question is will this happen? I don’t think it will ever happen because this current bitcoin network is near perfect of what a cryptocurrency or digital asset should be, we could only see soft forks or BIPs and nothing more.
But should that be the case, if it happens then it wouldn’t happen over night it will gradually change to zero and there will be news surrounding it’s fall so I wouldn’t be so shocked, i would have taken my funds off it by then.