it's unimaginable without paper money, this is the most popular form of money. People feel comfortable to purchase in regular life by spending money. It will be difficult to replace by any other form of currency.
So I believe that, future of Paper money is certainly certain.
Even gold could be replaced, fiat money has some advantages such as easy to carry on, instant transaction and divided into several values. Digital currency may have chance, but digital has some drawbacks, especially in the security problems.
I wouldn't really worry about security problems since the banks has been there for quite a while now and not much of them has got hacked. In the bitcoin world, you're on your own. Sure you can use an online wallet but you're just as safe as that online wallet is. If you use offline wallet, you're good to go. You have a physical item that you have to keep safe.
And since the digital currency like bitcoin has become kind of trendy these days, more and more people are transacting. And because of the nature of bitcoin, one has to put a larger transaction fee in order for the tx to be processed first before the others.