I don’t think it is, people are still active.

It was always expected that fringe servers might go down, while the core ones would consolidate

It’s not dead. Sure a few instances have gone down, for which I’m very sad, but it doesn’t mean lemmy is dead. Even with these setbacks I remain hopeful and still believe in the fediverse.

Not sure what instances your chosen communities live on, but lemmy is very much alive for me