Bitcoin will never replace the dollar, but it can become a real currency with at least something secured, unlike all other currencies. After all, they (currencies) are issued by central banks and even private banks (as in the USA) for their national purposes. Bitcoin is untied from national borders, so in the future it will keep the dollar company on the financial "Olympus" - this is obvious to many today.
I don't think btc will replace the dollar in our lifetime. As it is decentralized, the government can't have the full control of its circulation. And most governments prefer to have control with their financial system. Some may adopt it as legal tender like El Salvador but I don't think we will come to the point that btc or crypto will replace the dollar in the international market. I like the optimistic view here but we need to be realistic with our outlook.