Bitcoin will always be in existence as long as blockchain technology is in existence. No body should ever think that any coin will overtake bitcoin. Most of those people that will come up with and ideology and tell the whole world that it will overtake bitcoin, it is just a marketing strategy.
That is also how I see it, there are a lot of alt coins now coming up in the cryptocurrency market but still bitcoin remains number one despite those numbers and as we can see bitcoin still has the highest value. Bitcoin has been developed over the years unlike other coins which is just starting I think bitcoin has gained the trust of a lot of investors.