Lack of growth does not mean death. That’s a capitalistic mindset. It’s entirely possible for a community to be sustainable based on the people it has and have no need to grow. Lemmy’s not trying to sell a product; there’s no need for it to grow. People can join if they want to, and people can leave if they want to.

In terms of actual future prospects, Lemmy seems fairly large to me, and regardless of whether its userbase is growing or shrinking, it would have to shrink by quite a lot to become “dead”. Especially as Reddit continues to enshittify, I imagine its userbase will only grow. Hard to find social medias of this nature otherwise; almost all other social media is based around following people, not communities, and also obviously most social media is much more commercialised, less anonymous, much less text-friendly, etc, so link aggregator/Reddit style social medias fill in a niche people want and people who want a social media in this niche will gravitate towards the one they see as the best social media for whatever reason. Maybe Reddit because it’s the biggest, maybe Lemmy because Reddit is shit and Lemmy is federated and open-source, maybe their niche alternative because they’re part of a specific niche community that uses different software, who knows.