I have said it before, yes, people might leave. But the kind of people that stick so long to a dying platform are the ones that will never make it to Lemmy, Mastodon or whatever fediverse alternative you have.
None of these federated platforms employs any dark pattern algorithms to keep users engaged and clicking as much as possible. The kind of user that stays until the enshittification is not bearable anymore will not like the way the fediverse operates. So they go to some other place. Maybe its Facebook again, maybe Instagram, who knows.