it can perfectly work in conjuction with it and be vastly adopted
Yes bitcoin does not need to replace fiats to get it's own future. Along with fiats there are big possibilities to become more successful in terms of value and user base, like people use fiats for some purpose and bitcoin for some other purpose like online transactions or as investments.
Yes both dollars and bitcoin will exist and will serve the human beings with their own features.
People may argue that bitcoin has all the features of fiat currencies. Then what is the need for fiats. But all the people in this world does not have knowledge on Internet and crypto-currencies.
You got the point. To replace dollars, bitcoin needs to come in physical form. Otherwise all the people in this world need to have internet and knowledge on cryptocurrencies. Without knowledge on internet and online transaction, it would be hard for bitcoin to replace fiats