I was recently told Doomed Forever forum is closing soon. Never been there, but was told it used to be huge. I don't think any forums value should be judged by merely "activity". Most of forums that have most activity, appear to have top threads like "post pic of yourself" or such. All the casual talk with little if any relation to subject matter. I would guess that there is mostly gap between those who think internet is serious business, and those who don't, hah. If latter one dominate, first mentioned will leave.
That said, I'd rather see next someone start or participate in recommended Sounds of Pig tapes -topic, than "this mornings coffee mug and..." style topic.
I personally do not think we'd be running out of topics. Bands, labels.. new and old. Huge amount of things what go totally under radar for vast amount of people and if someone would even merely mention them, we could perhaps see how "underground network" works. People recommending interesting stuff to others. Not only merchants and consumers.