What do we think of a time that may come when the fate of human survival will depend only on using cryptocurrency for buying and selling, because mankind may soon find Fiat currency is obsolete or of no value in their current environment perhaps due to world earth crisis or pandemic or war .
Your opinion is valid!
It's highly impossible for cryptocurrency to completely replace fiat currency, even if there's a war or global crises, cryptocurrency can't be the last resort to earning. It's either the trade by barter system is introduced again or a local alternative is brought to place.
Remember, to access cryptocurrency, internet, electricity and technology will basically be needed. And all these can't be accessible if there is global crisis.