TSL is down compared to years ago in all demos, mostly because of PPM, not a fundamental change in listening. And younger TSL has fallen more than some older demos, not surprising when you realize that it's not just iPads but 120,000,000 gaming consoles and 500 channels of TV and so on. But the fact remains that radio is quite viable, and even if the 20-year projection is grim, there is time, as BigA says, for broadcasters to move the brands to new means of distribution and to new brand extensions.
There has never been an economy where every station did well. Even back in the "Happy Days" of the 60's about half of all stations either broke even or lost money.