Cash will never trash because it was the currency use by everybody young kids,adult,poor and rich every one using it and everyone is trying to do hard work just to get cash to be use on their everyday life. Even now that bitcoin is still moving upward,if you need to cash out your bitcoin and other cryptocurrency you are going to convert it into a cash so that you can use it.
It will be a long journey before cash will be obsolete. But right now, a lot of people are still dependent on using their cash. We may be in the digital age, but a large population is still not yet ready to fully convert themselves into cashless beings. Most of those who are residing in the countryside or remote areas are not bothered by technology, so I am guessing they are one of those that will stay in fiat money.