The need for fiat currency is currently maintained in many countries but I think it will gradually be abandoned. I was quite observing in terms of raw materials and real ownership of money between the fiat and crypto currencies.
1. Fiat currency requires special raw materials and this will continue to grow and will eventually run out, if so what happens is the sustainability of fiat currency? Crypto does not need this raw material because they are non-physical and no longer cost to procure raw materials.
Fiat money already exists mostly in digital form, and in some countries like Denmark or Sweden (not sure here), they are going to remove paper banknotes and coins from circulation altogether within a certain period. So creating fiat in the majority of cases doesn't require anything "material", technically speaking. Besides, modern paper money is made from cotton (and linen), not from wood as many mistakenly continue to think. Though I agree that it is a complicated process but definitely not because of "special raw materials". There is nothing special about cotton.