Bitcoin is just a product of technological development and technology is still developing, even tends to develop at a faster rate. So I also agree that bitcoin is not immortal and there will come a time when something better will be created to gradually replace it, just like what it is doing with fiat money, gold...other traditional assets. But one thing we can be sure of is that it won't happen anytime soon and the process will be gradual, not sudden. So if we can live until then, we will have enough time to adapt.
Looking at the overall development of the cryptocurrency industry, it is true that no altcoin can replace bitcoin shortly but anything is possible.
Because alts search for profit, not some set of ideals or concepts to push for - unfortunate, yet logical.
Because it's natural that everything that was done after BTC saw through the ideas that can be utilized and be profited from (in the perspective), whereas BTC shot high, without knowing whether it would pay off or not.