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.
I agree with you, it will cause harm if cash is remove. Cash will never extinct even though electronic currency are spreading and many people are using it. Eliminating cash will do harm on other because there still services that needed to paid by cash. And just in case if people lost their private key or anything that have access to their wallets, they money will be useless.
If paper money vanishes now, the troubles that will be caused are very obvious but if we talk about 20 to 30 years from now, I think cash won't exist or maybe only few people will have cash just for the sake of collection. Maybe we will have museums for them also like now our ancient human coins are kept safe. Some people may think I am out of my mind but this is the truth. Digital currencies are the future.