You got the OP wrong, he said that the people around him think bitcoin can't last longer than 14 years, not he said, he believes bitcoin will last forever. As for the existence of bitcoin, do not rush to confirm anything because the future is unpredictable. Bitcoin can be created to change the financial industry and the future of paper money will soon disappear. That means that in the distant future as technology becomes more advanced, it is understandable that a currency better than bitcoin will emerge.
But don't worry about that because we won't live to that point either. The thing to do is to focus on the present and that is to accumulate as many bitcoins as possible if we want to have a good future.