Bitcoin will die. Same with any other currency, if there's no one using it, there's no reason for it to exist.
With no one spending Bitcoins, there wouldn't be any transaction volume. With the no one trading on the market, Bitcoins will be worthless.
Such scenario won't occur. Without Fiat or some form of financial system we cannot have a living in these days. Bitcoin will be used more by the users who feel convenient as well know the truth of better we use better will be its growth.