There is always going to be a market for physical representations of art, whether that's a painting, photograph, sculpture or music. This is why cassettes and records are having a renaissance. CDs are physical too, but the music is still a digital 'intangible' file. Vinyl is based in physics, cassettes are analog tapes. For the same reason why when you go to the museum, you'll look at a painting anywhere from 30 seconds to 10 minutes. You could see the same painting on your phone, but close it before really taking anything in. Owning a physical thing is a different experience from purchasing a tune online, which will look no different from the other tunes that were pirated. Will it last? I think the cassette thing is a fad. Vinyl might stick around a bit longer. Digital is pretty much the best it's going to get. 48K 24B Stereo or Multichannel .wav, anything more than that and you'll be hard pressed to find anyone who can tell the difference. They might make better algorithms to make their file sized smaller, but why? HD space is becoming an issue of the past. Digital has peaked. If I were to guess for what's next, somewhere is going to invent a superior vinyl, a physical representation of music that has a better lifespan and occupies the same frequencies as digital. It will be large enough to allow for beautiful artwork but thin enough to store with a bin of others.
You hit on all the points I was going to make. I don't think vinyl is much of a fad, but I agree with cassettes to an extent. There will always be a niche market for them, but I'm also a person who will pick up 8-tracks from thrift stores from time to time so... People like to have a feeling of ownership over their music, and the tangibility of that which is provided by physical media is lost entirely when you're dealing with digital music. You can walk into a persons apartment and tell a few things about them by looking at their music collection if it's physical, and it's a point of pride for a lot of people.