What could happen is what did happen to XMPP / jabber.
Google embraced it for its instant messaging app, then after it had become the provider with the largest user base of said standard, it simply changed the underlying tech it used and stopped using the standard. To google users, their weird contacts that were not on the google ecosystem simply vanished, but they were a small number of people. To the users of xmpp servers, many of their contacts on the google side of things became unreachable again.

Now that's a thing that can happen if threads.net becomes the largest fediverse instance over time and loosing access to these users is a big detriment to users of other instances.

However, I couldn't care less if I lose access to the posts of threads.net users. I don't intend to interact with them at all. I don't use any mainstream social media at the moment, and I don't miss the ads, the drama, and the "normie" users, for lack of a better term.