I don't think we're anything close to anything disappearing, but I can see the industry continuing to evolve (and rationalise) as it has been doing.
Industries do change, if you take the ~40 year period since Alton opened and look at some specific examples, they can be unrecognisable.
@WillPS using the music industry is a good shout, look at tobacco, look at pubs, look at aviation etc.
Also, something that doesn't seem to come up very often in the analysis is Smiler and (much) less so, Splash Canyon. I have had so many conversations where when I mention parks/rides, or someone asks me something, the safety of the industry and even the concept of a roller coaster has been called into question - on the face of it, without a full understanding of the facts, it's a real turn off for some people, understandably so.
Industries rarely disappear, but it's also rare for them to continue in the exact same way, at the exact same scale forever.