For me, its gonna be hard to stop using cash especially in a world where we use money everyday for such a long time. I think its gonna be really cool and convenient if we are gonna use cryptocurrencies to every transactions that we do, but I think replacing cash or paper money is gonna take along way before actually happening.
I think cash and bitcoin will go together for a long long time. It is depending on the interest and usage of the people, if all the people of the world will stop using fiat and will give more preference to bitcoin then we can expect that fiat will extinct, but it do not seems so easy, because not all the people of the world so much educated to know about computer and internet and therefore it is not so easy for them to use bitcoin. Therefore we can say that it will take a lot of time and it is not so easy as it look like.