Yes I think so, Bitcoin will replace dollar in a few decades if things goes smoothly without any problem.
Things?
If Bitcoin is really a currency, then it is the highest valued currency in the world right now. Unfortunately, many people are using Bitcoin as an asset, not as a currency this is what is holding Bitcoin back from becoming a real currency.
But bitcoin is a currency, people are holding and saving paper money too and yet nobody is calling that asset.
So yes probably in couple of decades Bitcoin may replace Dollar.
I don't think so because it is almost impossible to control it. We will be facing lots of tax evades, frauds, money laundry in larger number than it is the case with money and governments won't allow it to happen.