Bitcoin will last more then any fiat currency.
So how old is the USD, UK pounds, EURO, CAD, YEN, YUAN, and your paper money? And how old is bitcoin now?
You can't buy a pack of cigarettes using BTC right now because of high transaction fees. Paper money or fiat currency doesn't need transaction fees when paying what you buy on any groceries.
You are right, bitcoin isn't replacing paper money anytime soon. The protocol itself however can survive for all eternity as long as even just a handful of people continue to use it. So far it has failed to show itself as a useful currency though but that won't stop people from using it.