If the question is, would Bitcoin become the reserve currency for fiat? If all people start using Bitcoin then it could be. But I don't think that governments would allow that to happen. During the huge price surge that happened more than a year ago most governments around the world started putting regulations on Bitcoin and some even banned its use.
This wasn't simply because they were trying to protect people from a very volatile asset or to protect against market fluctuations that Bitcoin could create, it was because they worried that they would not have control over the money supply, if more and more people started putting their money into cryptocurrencies.

Bitcoin can actually take on the role that gold had before it was unanimously decided that currencies don't have to be backed by commodities, many decades ago. If used for that purpose, it would have most of the advantages of gold, and almost none of the disadvantages.