I don’t know how federation works in detail, but I really hope it’s like torrenting where peers introduce each other. That way if one person decides to defederate with an instance it’s a decision that only applies to him. If anybody else is federated then the connection information is available to all. i.e. the network heals around damage.

I have no problem with someone constructing a bubble for themselves, but they don’t get to say what’s in my bubble.