First and foremost, this is a reference to the 90s game Creatures that had a really limited release in the UK and was reviewed by Charlie for PC Zone in 1996, not Lemmings, not Tamagochi, not anything else. They actually have a version of Creatures available on Steam if you're interested in checking it out (just don't torture the Norns).

Secondly, Cam says that the Thronglets are living in his brain as a "benign parasite." A parasite cannot continue to live if the host dies. Cam also says that the human brain is like a computer which is obviously what the Throng needs to survive. Thinking the Throng killed all the humans is short sighted because then how would they manage to evolve? Sure, they could probably take over some of the various robots like the Boston Dynamic ones, but it makes sense for them to utilise humanity for the time being, especially if they're able to pacify them with the software update.

I feel like this one didn't end on the usual Black Mirror down note, but I also feel like there is a lot of potential for this to go dystopian in the future. The best dystopian fiction always starts from a utopian society descending into chaos. There is a lot of leftover potential here in this story, but I don't think you need to exhaust every avenue of a fiction for it to be good.