I do not believe fiat can ever be replaced as the government exist.
The government could ban bitcoin so the value of bitcoin could drop to non existent to one's country
That is right, bitcoin will never be replacing fiats, even at the price of $10,000. We all know that government will never make bitcoin their own currency because I think they would rather make their own digital currency than make bitcoin their currency. And I think even the government ban bitcoin, they will still use bitcoin, no one will never know that.