Defeating fiat is like a whack-a-mole game. Fiat has lost many times in various countries over centuries, but it's still here. When fiat finally caves under the burden of its own issues, overdebtedness of the economy, etc., there will be a reset to another form of fiat, crypto currencies can gain a bigger market share as people lose confidence in fiat, but defeating it completely is unlikely, even if Bitcoin didn't have the flaws it has, it's still unlikely.
Fiat hasn't existed for thousands of years.
The Chinese tried unbacked paper currency = fiat many centuries ago, long before Europeans did. They pretty much invented this concept. It could be just
a thousand years, not thousand
s, still it's a widely known concept to them.
Like you said all fiat systems always comes to an end. How long do you think people will keep doing this now they know they have an alternatives? By the way your confusing money with legal tender. Even the Chinese in history understood Gold etc needed to back paper money.
Let's say the Dollar and various fiats died next week, all the people unless they were holding assets like Gold or tangible assets and Bitcoin owners are safe and even prosper. It wouldn't take a genius to know what the image of abitcoin would be after such an event. Bitcoin won't die it will grow like a virus till it infects the whole world. The future if sound money wisely is part of it will be based on digital currencies backed also by governments and Gold.