People are fearful then meta will retract it/ defederate and take the majority of content with it (EEE). This would effectively kill the fediverse.
I don't see how that could possibly happen. It's not like they can buy the Fediverse. Seems to me far more likely that the Fediverse will be gain interest from people wishing to follow/interact with Meta users without being beholden to Meta and if/when Meta decouples from it again the Fediverse will be larger than before. Sure, some may come and go, but others will find interests outside of Meta.
Like everyone is pointing out, they already will be the largest instance. They are not going to gain that much by trying to trying to absorb the rest of people who are likely in the Fediverse from dissatisfaction with Big Tech and wanting to break free from their algorithms and restrictions.