Almost, but not quite. If lemmy.world doens't defederate from beehaw (it's a two way thing) then you can still see all their posts, and interact with lemmy.world users on those posts. But beehaw users, and users of every other instance won't see your comments, and you won't see theirs.

I'm not saying nothing is lost when an instance goes haywire. But, it's certainly much more robust against those things then reddit. How much have you lost by not being part of beehaw? Something, but, it's still a very good community.