I do not agree. Actually, Bitcoin and fiat money is a coin with two sides, they both exist but in a different way, meaning that each has his own way, both need each other. What would happen if Bitcoin without fiat money, to be exchanged for what? Is the community as a whole are familiar with and use Bitcoin in everyday life as a means of buying, selling and exchange? So I think it will remain Bitcoin as Bitcoin and fiat money as fiat money
And why would they need each other?
Fiat has existed without Bitcoin by its side for a few centuries and would most certainly have existed without it for a few more centuries being no worse for the lack of Bitcoin nearby. Regarding Bitcoin existence without fiat, it is assumed that it will be exchanged for goods and services in pretty much the same way fiat has been doing that for all these centuries. In fact, this is the exact purpose which Bitcoin has been conceived with, i.e. to be used as a full-fledged currency not depending on any fiat as an intermediary