I think we need to ask this question separately for the microblogging fediverse and the "threadiverse" (i.e. Lemmy-compatible communities).

The microblogging fediverse isn't dying, I scroll through it every day, it's one of my main sources of news (some of which I then post on Lemmy). I wouldn't be able to keep up with much more than what I currently get into my feed there.

The threadiverse meanwhile could definitely use much more activity. I hope it eventually becomes a place to discuss even the most niche topics imaginable, like web forums in their era...