I guess we will see everything fall and bitcoin rise

I dont think it will drop below 400 in the next 8 months.
you are right bitcoin is really increasing its price too much higher and bitcoin adoption is going to increasing too much faster because people strongly believe in bitcoin.
After 20 long years bitcoin can replace fiat. As long as there are believers bitcoin can go on the place that no one expected. Bitcoin will be the base of all fiat and crypto currency.
I bet you on that, it will not happen. I am sure after 20 years dollar will still in the circulation but I doubt bitcoin will still be progressive that time or there will be new crypto currency that will take over the position of bitcoin.
You are right, we have to believe but we should reserve some doubts as well, especially when you are comparing it to a more stronger fiat.
Selling today is not going to be a good thing if you are holding a lot of bitcoins. You just need to be more patient because the price will increase as we wait for its continuous fluctuation. But I don't think that 20 years from now bitcoin will replace that is a different thing. But if you will just running for profit, just wait for the right time.