Assuming you mean “Can Mastodon instances defederate with Threads?”: Yes. Mastodon (and similar services) run on the ActivityPub protocol, which allows them to decide who they do and do not federate with. Many instances have chosen to preemptively block Threads, many have chosen not to. Pick what works for you.
It’s based on assumption, not faith. If we can trust our senses, and if things will continue to be as they have been, then the things we are learning have value. As long as you can recognize that everything could in theory end or completely change at any moment, it’s not blind belief.