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survival will depend only on using cryptocurrency for buying and selling, because mankind may soon find Fiat currency is obsolete or of no value in their current environment perhaps due to world earth crisis or pandemic or war .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.
And people should not forget that there are other valuable asset which lots of people more comfortable to deal on rather than Bitcoin.
That's why its really hard for Bitcoin to reach on that status on where it can replace fiat since first its volatility is one discouraging factor especially for those people don't know how to deal with this coin. Also I don't hope that to happen for now because for sure there are lots of technicalities would gonna happen before such event would come.
If that crisis will happen on which there's no internet globally I guess people would prefer Gold and Bitcoin will be in freeze until the situation will go back to normal.