Even if we defederate with them they can still grab all the content here. Defederation just stops the flow of content from their instance to ours. Defederation just hides the comments from Threads’ users on our discussions.
I think the real test is when they start demanding that other instances start moderating their content to comply with Facebook’s terms of service and if not then defederate and make them unable to communicate with the by-far biggest instance on the fediverse with almost all the users.