Actually I don't think crypto will ever replace fiat, I think they will co-exist to serve different purposes.
What is your opinion?
No, it won't. No governments would allow that to happen.
This.
And it really IS impossible in today's world for Bitcoin (or any other altcoin) to replace fiat currency. Not in the next 100 years at least.
There is too many things that common people use fiat for and I don't see them switching to Bitcoin any time soon.
Both fiat and Bitcoin have its advantages. Use them together.