Ahh, good point, yes.
I actually was thinking about those beautiful little deep-sea worlds when I wrote the above, but simply didn't know enough to assert a dang-ol' thing at the time. Okay, let's see:

However, although it is often said that these communities exist independently of the sun, some of the organisms are actually dependent upon oxygen produced by photosynthetic organisms, while others are anaerobic. --WP

So... looks like we have at least *some* members of these little communities carrying on, past the death of oxygenic photosynthesis, which they evidently don't need in order to survive. (meanwhile with anoxygenic photosynthesis carrying on for many millions more of years).

But off the top of my empty coconut, it does raise a couple Q's:

Since there are maybe a dozen or less community members who live in these little worlds, closely built in to a commensurate ecosystem, would the death of the ones who rely on traditional photosynthesis bring about a collapse, either partial or total?
Would rampant global warming tend to mess with the already super-heated, typically sulfurous nature of these worlds? (me, I would tend to think "nawt," since they're already so hot, but then again, I'm just some layperson really curious about all this, hah)

Ah... those beautiful, entrancing little forbidden worlds:
https://www.youtube.com/watch?v=ECBbAjoEHWI

❤️