I am not sure . dollar and fiat currencies still has its own strength. I think bitcoin and the dollar could together build a system in the world economy. dollar became the main media in the real world and bitcoin as the main currency in the digital world.
Dollar is only depending on the petro-dollar system and once it falls, dollar may collapse. it is just a matter of time before that happen. but bitcoin wont replace it. a new fiat currency will emerge and people will trust it again
I think that is not possible for the people are going to keep on using dollar as they are able to use it for a long time until now.
And it is going to be a culture shock if the government is able to replace the use of dollar immediately.
Because not all the persons who uses dollar will able to use bitcoin immediately if that is going to be implemented.