if the dollar goes to zero, that would pretty much mean no one has a job. who wants to work for $30 per hour when a loaf of bread costs $1000? owning bitcoin won't change any of that.
Of course owning bitcoin will change that.
Take any country which has recently experienced rampant hyperinflation - Zimbabwe, Venezuela, Argentina, etc. It costs billions (or more) of their local currency to buy a loaf of bread. So what do these countries do instead? They use a different currency altogether. Maybe USD, maybe EUR, maybe something else. All the people who owned this other currency prior to the hyperinflation event are in a far better position that people who are now trying to purchase this other country at exchange rates of billions to one.
If the dollar goes to zero, and it costs a million dollars to buy a single euro (substitute with any other large currency), but I still own a bitcoin worth ~26,000 euros, then I will fare significantly better than if I owned no bitcoin.