I also doubt will dissapear as long as we have people who use it, miners and nodes who will maintain network on and exchanges and merchants who accept it bitcoin will have long life.
Bitcoin is Finite no matter how long it takes bitcoin will eventually ran out one day but before that happens a new cryptocurrency will probably emerge that will be able to replace bitcoin. it may not be as good as bitcoin but it will be the one who continue the Bitcoin legacy.
Bitcoin's notion and concept is great but I think it is now the best.
There are many better projects and cryptocurrencies than Bitcoin. Bitcoin is just the first and the most trusted right now. If all coins are lost one day there could be a fork and the chain can come back to normal easily.