The real money will disappear but not because of cryptocurrency because of electronic payments .Now a days most of the peoples and shops are accepting electronic payments.i hope within one or two years electronic payments will spread all over the areas including the deep villages also.It does not mean that real currency will disappear it will live in the electronic currency.
I wouldn't see that as real money disappearing, it's just like the age long transformation money have been undergoing. Dollar from your card is still dollar and they won't make much sense if there are no more physical dollar. Likewise, cryptocurrencies are useless without real money, so they more or less compliment each other.