If everyone in the world gets into crypto and cryptocurrency will become an official global currency, do you think bitcoin then will stop depending on fiat currency? Or will it just co-exist with fiat?
This is an interesting and it's hard to say, depends on really what happens in the future.
It can of course coexist, there is place for every preference in this world now and each one of them who become popular have their millions of users - It can also be inside the stock market along with all the other investment coexisting with them.
However, unless a new law comes into place there is no reason why fiat would disappear for good.