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?
That’s correct, any thread starting with a Meta comment will disappear from your perspective.
On the other hand, assuming Meta hasn’t defederated mander.xyz, Meta users could still see and comment on posts that you made on misguided.ml. You wouldn’t see any of their comments, but users of misguided.ml would be able to.
Federation is a bilateral agreement