It is almost impossible fiat to be replaced with crypto. Once the governments see all the advantages that comes with the blockchain tech probably fiat will become crypto.
I think it can happen but sometime when it happened because in various parts of the world fiat money is still being used ... moreover about people who are unfamiliar about crypto they will find it difficult to accept the need for an approach to all groups
I think for Fiat to be Crypto has a high difficulty. where with crypto the government cannot regulate it. and whether the government is willing for this. because until now no government has volunteered it, even though it legalized crypto