Bitcoin, for now, is not suitable to become a national currency of any country. Bitcoin's value is too volatile so a product or service will always change in price with respect to the price of Bitcoin. Also, a transaction fee is there with every transaction, this is not practical in using in a daily basis. It will be hard for the government to control the scenario. So if a country will make Bitcoin as its national currency then they have to regulate it first.
I also believe so. The fiat and Bitcoin system should work together since they have their own specialty like fiats are more like having an instant or urgent transaction while Bitcoin can be used as a mode of transaction in an international scale so you won't need it to convert from one fiat to the other. I wil not elaborate more.