Without altcoins, bitcoin is dead too. I don't believe that altcoins are going to disappear. Some are surely disappearing, but not all of them. If people persist to only put money into bitcoin, everything is going to fall little by little, as blockchain companies are going to go bankrupt. And without any blockchain companies, bitcoin is going to die too.
Bitcoin will definitely not die without altcoins, but I think that no one in this market, specifically large players(whales), will not allow the altcoins to die because now it is their main source of income