I believe that btc will continue to work in the current system same as with fiat money. While cryptocurrency will grow rapidly, I believe that fiat currency will not be replaced by any cryptocurrency since it both need each other. People buy cryptocurrency using fiat for their investment and once they sell their cryptocurrency, people will have it change to fiat currency.
It will be adopted and updated, current system will do adjustment to adopt this scenario to be able to add and fulfill the needs to use blockchain and crypto for their benefits.