Fiat has been proven to be stable for a longer period of time since we are still using it, maybe I will believe that some investors will transfer their money in bitcoin but not to do away with fiat, they still need fiat as more than 99% in the world population are using FIAT.
Thats why an option to buy bitcoin is for those who has sapre money to do so and for a person who are well aware of internet and cryptocurrency. Still fiat is king, everyday we used it and still it it is needed in daily real life transaction. Even bitcoin is @ $10.00 fiat is still stable and important.
And that's will make fiat still worth it and for bitcoins adoption today still we all know that stores are very limited to those who are accepting bitcoins. It won't make fiat worthless even the value of bitcoin will be even higher as $100,000. Because it has been used for many years already and the people is trusting it more rather than bitcoin.