They may make their own instances, but depending on the content that comes from them, they may even be defederated from ours.
It is WEIRD how much I feel like I've been here before.
My first days on the internet were around the time that both email lists, and IRC chat, were popular. IRC chat was a bit more centralized than this perhaps in management, but in many ways the concepts were similar: multiple servers, interlinked, and if the admin of one server had a problem with the admin of another, they could delink from each other. IRC, a protocol that was popular 30 years ago and has been largely dead for at least 10, was basically the OG fediverse of instant messaging.
Anyways, there's a massive amount of promise with this. It's more or less what Reddit was originally meant to be: Each team fully in charge of their own subreddit, and Reddit admins only there to make sure that each subreddit played nice with each other subreddit. In a fediverse context, it's almost exactly the same, except the responsibility for cutting off subreddits that don't play nice lies with the managers of each "subreddit" (instance).
I realize that instances are not magazines and so on, and this analogy has technologically weak comparisons, but I think the principle works.