Only if people consistently choose to subscribe to Meta creators and communities over the ones on the Fediverse. It's not like people here will be auto subscribed to whatever infiniscroll algorithmic slop Meta is serving. Meta can't forcibly implement that into other instances.

If Meta means to use the ActivityPub as a selling point, they need to show at least some of it to their users. But if they give up entirely, then there's no need to worry about defederating anyway.

That said I'm not naive and I expect that Meta will try to play dirty, but it seems to me like the extent of what they can do is pretty limited by the decentralized structure of the Fediverse. They can't just take other instances over, unless they downright buy the admins, and that's a whole separate matter than federation. If they do, still, it's trivial for users to jump into another instance away from Zuck's scaly hands.

But even then, if it's so easy to attract people away from the Fediverse, then it means that there is something it is lacking, and that's not going to be solved by being reclusive and trying to stay beneath notice.