I also do not believe that traditional currencies will leave our lives, but I think that the cryptocurrency will be able to work with Fiat money on a level. I think I still need some time passed people to take bitcoin as a forum of payment.
It will be gone but not so soon.
cryptocurrency will definitely replace them, though this need more time of waiting as there are so many people who dont know what it is and how to deal with it.
But definitely in the future it will. different countries will have their own crypto.