I think it's impossible to happen. Because as good as any bitcoin never replace dollar as international currency that applies in any country. While bitcoin, it always exist as a digital currency only, no more.
I do not think that it is impossible, because to me i think everything is possible in this world, But it i think that it is not such an easy job, because USD is one of the most poplar currency fo the world, and most of the people are giving preference to USD. i think when the users of bitcoin will increase then it will really become more popular and may be in next few decades people will be still depending on fiat.