American have dominance economic from other countries and make their money value have higher price, maybe when their country not have many power full make their money value will be down, but if many countries want to use bitcoin I think USD of american money left the name and many people or companies want to accept bitcoin as currency payment.
Fiat will never stop being here. It will be there even if bitcoin or crypto is accepted into payment systems wide and beyond. Fiat is the biggest mode of transaction even today and there are people who are not willing to accept crypto because of ignorance of what actually controls it, its bad reputation smeared by yellow journalism and so on. Older people are very less likely to accept it too but they will die out soon (
However the time at which fiat and crypto usage reaches an equilibrium is far from now. Currently we should focus more on adoption and acceptance of bitcoin in different marketplaces.