As far as we know life is only present on Earth, we presuppose that in the vastness of Cosmos there are other instances of it or that it can re-emerge from almost zero, but the reality is that we simply don't know. So maybe there is a possibility that wiping out all the life on Earth also wipes it from the entire Cosmos, forever.
Or perhaps the comment you were responding to was asserting "knowing" or "caring" is not something Nature can do.
I care and I'm part of Nature.
The comment was paraphrasing the message of the poem "There Will Come Soft Rains" (which Bradbury used for the title of his story), which is exactly about this: that Nature won't know or care when we're gone.
"Humanity" is far from "all the life on Earth". Nature will be better off once it happens.
I see this a lot, and I think it's sort of naive. Nature itself is doomed due to the way the universe works. It's also far more brutal and arbitrary than we could imagine being. The only way to even have a chance at avoiding the doom that "nature" is facing is for something to evolve that can manipulate and forestall this inevitability.
I don't know if humanity is what can do that, and likely nobody knows. But nature is not going to survive either once you broaden the time horizon a bit.
> Nature will be better off once it happens.
As long as "it" happens before we poison or otherwise harm our planet beyond some "tipping point" after which Earth becomes "inhospitable" to most/all "complex" life in general.