I believe that bitcoin will never replace fiat because fiat is a well organized money and fiat system is supported by every government around the world and each money that a country have has its history behind it.
No, it is not good to say the fiat is a well organized currency, as fiat is only a fiat used by the people and governments for their use only, the only thing is that it has a strong support, but not have any organized method for it to maintain.
The value of fiat is decreasing and it will decrease in future too, bitcoin is the only currency whose value keeps on increasing over a period of time.