"Radio goes through phases."
It also tends to rely heavily on imitation and station managers jumping on bandwagons.
Many, many years ago, there were about three music formats. Then the formats divided, sub-divided, and now there's an alphabet soup of acronyms for different music formats in which the differences are so subtle that only an industry insider can tell the difference.
Talk radio wil probably follow the same path. "News/Talk" will subdivide into several slightly different variations, as will "hot talk". In a decade or less there will probably be a dozen different categories on this website for each slightly different talk format.
There will be a format for "lifestyle talk", such as what Dr. Laura does. There'll be a format for political talk, divided into liberal and conservative. There'll be sports talk, subdivided into spectator sports talk, "adventure" sports talk, local sports talk, and possibly one other sports talk. There will be tabloid talk stations full of interviews with celebrities and taped segments of celebrities saying stupid things (the audio equivalent of papparazzi pictures). There will be religious talk stations, subdivided into fundamentalist/Pentacostal, Mainstream denominational, non-Christian (Muslim, Hindu, Buddhist), and New Age.
That is the probable future of news/talk radio, regardless of whether Limbaugh or Laura hang it up or not.
Each of those formats will probably develop some dominant hosts, but whoever they will be, they'll probably be people who aren't currently well known on the radio.