Bitcoin's life span is determined by how high its demand is to the people. As long as there are people who utilize it as medium of transaction, then it will survive for a long time. As of now, bitcoin has already established a good reputation to the market and has unleashed its potential when it comes to business so I guess it will last long. Of all the cryptocurrencies existing, BTC is by far the most popular and the most trusted coin. Therefore, I believe that it will be circulating around the market for quite a long time.