People apparently forget that if something very bad happens, whether it is a global war or a major natural disaster, we can expect that there will be serious disruptions in communication or, better said, an interruption of the internet. If that happens, the things that will be most valuable will be food, drinking water, and medicine, and of course, means of self-defense.
Of course, we should not be pessimistic, just realistic and prepare in time for every possible scenario.
I don't think that if such a time will come when fiat will become obsolete and the human race would depend on only cryptocurrency as a means of investment, transactions and survival that holding cryptocurrency would be our priority. It is different when people decides to hold cryptocurrency out of their free will because fiat have failed them than being compelled to hold it because they don't have a choice.
If things degenerate to extreme level because of wars and destabilization and fiat where to become of no value and use to us I think that survival would precede holding cryptocurrency. Constant electricity and internet might not be available so crypto transactions would be affected, what would be priority would be food and clean drinking water. But if electricity and internet are still in place then cryptocurrency transactions can be enabled but there has to be commodities to buy and exchange your cryptocurrency with.