Fiat currency is issued by governments. And let's face it, no government has ever really attained immortality. If a government falls apart or gets replaced for whatever reason then its old currency becomes worthless. When that happens that money is about as valuable as some expired coupons, nobody will accept it as payment anywhere.
But cryptocurrencies are a new kind of money, they're not issued by any governments, they're completely decentralized. And the money part is practically all they do. No government on Earth can 'overthrow' cryptocurrency, because cryptocurrency isn't tied to a nation that can just be invaded.
Even if all the developed nations in the world just decided to ban all of the cryptocurrencies at the same time, that would only change the supply and demand to make crypto even more valuable to everyone else. And then the folks in the "3rd World" countries would become rich while the folks in the "1st World" countries would become poorer by comparison.
Bitcoin has the political world stuck in something like a Chinese Finger Trap, the more governments struggle against Bitcoins, the more it clenches its metaphorical grip. If the governments of the world really wanted to hurt Bitcoin they should have just ignored it, because all the controversy only makes it more valuable.
Take into account that the Bitcoin is already worth thousands of times more than the Dollar, it's a clear sign of the high demand for Bitcoins. But more importantly, being worth significantly more than the Dollar means that Bitcoin has already "overtaken" the Dollar. At least on paper, Bitcoin is winning by a mile.
But the interesting thing with Bitcoin is that most of the people in the world either haven't heard of it yet, or they still haven't taken it seriously.
But either way, it's only a matter of time for people to hear about Bitcoin. And it's more likely that more people will take Bitcoin seriously as time goes on.
Also as time goes on, governments will have to face more and more challenges, problems like we've never dreamed of before. But crypto is about as logistically immortal as anything gets, it can only ever really die when the last password is finally lost and forgotten. Even if the electricity goes out in your country, or even the entire continent, your coins are still there, you still own them. You would just need to wait until you can get back online again before you can spend them. (And in the mean time you can still receive Bitcoins, even with your electricity out!)
The real "problem" with crypto doesn't have anything to do with any bubbles. It's an issue they call user-adoption. Right now cryptocurrencies (including Bitcoin) are in their infancy. It's a lot like the Internet in the early 1990's, at first it was just computer nerds who were using it, but then it caught on, and it spread like wildfire, and now almost everybody is online. When that happens with Bitcoin you'll be seeing everybody and their grandma getting into crypto.
So, how will crypto replace fiat? Crypto has already won the numbers (it's way more valuable than the dollar, and even gold), the rest is just a waiting game. If you want your crypto to make you rich then just get as much crypto as you can and hold onto it. Wait for more people to catch up with the technology. And wait for the technology to become more user-friendly. Because by that time the supply and demand mechanism will have raised the prices way beyond what anyone anticipated.
