It's rare for a medium to go away altogether. Certain uses of a medium will go away, and the number of media outlets will diminish. But I don't think even AM radio will go away. There will be fewer AM stations, as there probably should have been for the last 30 years or so, but some will still be around. It might even have more of a chance of going fully digital than FM since there will be less of an analog audience to lose at that point. FM stations will either go pins-up or will develop economic models less dependent on hard-to-measure (accurately) delivery of audiences to advertisers. In the online world, even Usenet is still around. It's in greatly diminished form, but it's still there. There are still people with aol.com email addresses. MySpace has a niche.
The one recent media-related functional technology that I can think of that's totally disappeared is photocomposition, which turned out to be a transitional technology between hot-metal typesetting and desktop (and direct-to-PDF/plate) publishing. Device-independent page description languages were transformational. Even so, Compugraphic, which was a leader in that field, still exists as a business unit within Agfa, though its product lineup is much different now. To be clear, all this came to fruition in the 1990s before newspapers succumbed to their own sets of economic pressures.