I don’t think we really know at this point what will happen or how fast reddit will fall. What we do know is third party app users will no longer be able to use the site. And that it will be harder for users with disabilities to effectively use reddit.
I am proud of Lemmy.ml for defederating. The second I find out if kbin social or lemmy world defederate or not I will just move to the other one since I use both. (Edit turns out Lemmy.ml is run by Tankies and also allows federation with lemmygrad.)