Fiat will continue to exist side by side with cryptocurrencies. For now there is no reasonable prediction that fiat would be replaced by cryptocurrencies. Bitcoin and others need technologies to functions. At least a mobile phone that is connected to the internet is needed to carry out an average bitcoin transactions.

A report indicated that a total number of 450 million people, about six per cent of the world’s population don't have access to mobile broadband coverage. Also,  3.4 billion (about 43 per cent of the world’s population) people do not use mobile internet despite living in areas with mobile broadband coverage. And this underdeveloped people are mostly found in Sub-Saharan Africa. https://punchng.com/450-million-people-lack-access-to-mobile-broadband-report/
How would this people handle cryptocurrencies transactions. They would ever embrace fiat.

Also most countries lack essential infrastructures that aids the usage of cryptocurrencies. Facilities such as power or electricity is lacking in most countries. Hence, it would slow the adoption speed of bitcoin and others and encourage the use of fiat.

Another challenge that would keep strengthening fiat is high rate of illiteracy in most countries. In some countries most citizens lack basic education which include reading, writing and arithmetics. These set of people would prefer to use fiat transactions that is much easier because they might not be able to understand the complexities of cryptocurrencies transactions

Summarily, some develop country might come close to replacing fiat with cryptocurrencies but most underdeveloped or developing countries would still hold firm to fiat because they might not have all that is required to make cryptocurrencies transactions smooth.

It is very certain you can never eradicate fiat entirely from the system as fiat must always be the commodity in exchange for crypto, since it's simply because we have got fiat that cryptocurrencies exist. And fiat is the only measure through means a country can be ascertained to be either rich or poor through the value of its currency and not crypto, because if all countries are to use crypto there will be more recession even than we have now. But however, that doesn't mean crypto adoption shouldn't be encouraged in these places, because crypto has come to stay weather people like it or not.
What causes a recession is when a country consumes more than they produce. When the goods or natural resources imported into a country is more than they export out to other countries, it causes a devalue of its currency leading to recession. So my typical advice is that fiat and crypto will always exist, and left for you to know the difference and take advantage.

Well, that’s just it; I think the people are only ready to fully accept whatever the government accepts as the legal tender. If the government in a country should accept Bitcoin as a legal tender, and remove their fiat currency (which has been the first and the original legal tender used for exchange of services and goods), then people will quickly adopt that.

But, as long there continues to be Fiat, people are not ready to fully adopt Bitcoin, it’s still going to be an asset or an alternative whenever they feel like using it.

Central banks can regulate the amount of money created with fiat money, they have more power over the economy. The majority of current paper currencies, such as the US dollar, are fiat. One risk with fiat currency is that governments will create too much of it, leading to hyperinflation.

Advantages
Fiat money serves as a good currency if it can handle the roles that a nation's economy needs of its monetary unit—storing value, providing a numerical account, and facilitating exchange.

Disadvantages
The mortgage crisis of 2007 and subsequent financial meltdown; however, tempered the belief that central banks could necessarily prevent depressions or serious recessions by regulating the money supply. A currency tied to gold, for example, is generally more stable than fiat money because of the limited supply of gold.

Ref. https://www.investopedia.com/terms/f/fiatmoney.asp

I disagree with you in that. Fiat won't always be the norm.
We've come a long way as humans and transacted commerce and accepted payments for services rendered. There were various means of payments and what was used as money before fiat came along. Change is necessary and like we have always evolved in our means of payment and what is accepted as money. A key characteristic of money is acceptability meaning it must be generally acceptable. Btc is slowly yet steadily becoming acceptably generally and would overshadow fiat in the coming years. Fiat would probably still be around but would probably be used as a second choice.

Better not to make yourself that hopeful for government to have some u-turn in speaking about cryptocurrencies which it would really be still focusing or ending up on throwing negative sentiments and feedbacks
or the worst do make out direct ban without any questions or reconsiderations but well this isnt something surprising for government to do so because it would really be something like this.
Fiat would remain no matter what and its true that crypto cant take over as long they are on the peak on the chain, Crypto would still remain as an alternative nor matter what.

Even if governments abandon their national money in favor of cryptocurrencies, I do not think that then citizens will quickly switch to using cryptocurrencies. There are still many problems here, and some of them are quite difficult to solve. However, states will never abandon their fiat currency. It is not even worth dreaming and fantasizing about. Cryptocurrency can only walk in society along with the fiat of states, and at the same time fiat will always be the leader. States have been a form of our social structure for many millennia, and for the full functioning of the economy, each state needs its own currency, which it can control. Other forms of payment can only be alternative.