They might dip their toes in at first. But then you’ll have 9 out of 10 big communities/users on Threads (or probably 99 out of 100 if we’re realistic). And at that point if Meta defederates nobody of those users will care. Threads will become Twitter 2.0 and be its own thing, while Mastodon will be crushed with a tiny user base in comparison (which will get even smaller because most content is on Meta servers, so users switch over to Threads).