Paper money, does not need internet to operate. Bitcoin does. Some have created Bitcoin coins, with a private key embedded, but people did not rush to use them. I think that there will be many types of money. When we need to pay locally, paper money is the best, because you don't need any infrastructure to operate. When you pay online, you cannot use paper money, so digital cash is the only way. I don't know if Bitcoin will be the most used digital cash, but it will find it's place in usage.