I think there are good reasons to not let corporate interests join the space we built to escape them, but I guess every instance is free to (de)federate with whomever they want.
So let’s say my instance (mander.xyz) defederates from Meta but another Lemmy instance that meander.xyz federates with (let’s say “misguided.ml”) does not. What happens when someone from Meta comments on a post from misguided.ml and others from misguided.ml comment on that comment? Will I see the comments on the meta comment, but not the original meta comment itself? Or will I not see the entire thread?
I believe how it works is the comment from the user on the defederated instance and ALL child comments of it do not show up on your instance. So it’s as if that conversation just stopped after the last person from an instance that you’re federated with commented. You wouldn’t see anything from defederated commenters or the replies to them, even if they are replies from Instances you’re still federated with.
Login to Beehaw and check out a post from a Lemmy.ml community on it, and then look at that same post while logged into Lemmy.world and you should see the differences - because Beehaw defederated from Lemmy.world.