TV isn't going anywhere until the internet becomes completely free and covers the major countries of the world 100%. Until then, millions (probably tens of millions just in the us alone) of people that don't have/can't get/can't afford internet, and millions who have internet still watch tv and probably will continue to do so for a long, long, long time.
It's definitely on the decline. Who wants to be forced to watch entertainment on the networks' schedules? Ever since the TiVo allowed for easy and reliable time-shifted viewing (without having to set up a VCR and timer), the idea that advertising revenues will pay for TV programming has been superseded. Entertainment producers will always go where the eyeballs are, because they have to. If the majority of eyeballs are on the internet (and really, they are) then that's the place for everyone to display their stuff. TV will still be around in the same way radio and smoke signals are still around, though.