It is clear Facebook have targeted a select handful of very influential people within the fediverse and it appears they have had some sucess in convincing some instances to federate with them or at least to make supportive comments. But when Mastodon has 20,000 instances and lemmy has 1,000 plus it is inevitable that a small number at least will agree to federate. The best thing to do is to be vocal about opposing Facebook and to threaten to leave your instance if they do federate. The fediverse can survive a hostile interloper but it will have to be pro-active. (Four years ago it rallied around a campaign to oust Gab. It suceeded completely).