I think that while cryptocurrency evolves and more and more people will use it fiat money will crash some day but I dont believe that this will happen in the next few years as some already said fiat is backed by the government and 100% of the citizens of each country use fiat while only a few million in the world use crypto.. so I think it is just a question of users and trust... most people dont trust their government and when they start to use crypto instead of fiat, fiat money is doomed and will crash for sure.