Total removal of fiat from the society will do more harm than good.
No matter the level of technological development, not everyone will be able to embrace cashless transactions. And also, most services need to be paid in cash.
We don't really know what new technology may come out in the future though. It's possible that somehow in the near future, everyone will have instant access to a bank account or some form of savings account that they can use instantly with some piece of technology. For now, however, I agree with you that the removal of fiat would not fare well with society.
There is another reason for which I strongly believe that paper fiat can't go extinct. At least, not in the next couple of decades. Even as it stands now, not too many people know how to use a credit card or engage in online banking let alone mastering the complex process that is involved with cryptocurrency. What happens to the illiterate and out of fashion old citizens who can barely read and write? How are they going to survive if paper money goes out of fashion?