Its not impossible, but the chances are very very low. Yes, bitcoin's price is skyrocketing due to it's high demand, but still there is a large percentage of the population that doesn't have any idea about bitcoin or cryptocurrency itself. Many people, especially those who are digital immigrants, mainly depend on fiat or paper money. We also have o change the whole system in every country if we want to change our currency.
Yup. Even the kids today are growing up using fiat and won't learn about crypto until they are older and some of their kids will be in the same boat. With that said, it will easily take over 100 years until everyone on Earth uses crypto, but eventually fiat will be faded out in favor of this more modern method of finance.