You should still be able to view and comment on beehaw as normal so you don't have to miss those communities. Defederation is a one way street. So it's just like lemmy.world doesn't exist as far as beehaw is concerned. We can't have any impact on their vote counts from their perspective, they won't see our comments regardless of the instance it's posted on, they can't visit any communities from lemmy.world, etc. But unless lemmy.world defederates from beehaw we will still be able to view, vote on, comment on, etc anything from beehaw as normal. It's just that you are less likely to get any sort of interaction so you are disincentivized from doing so. Technically we could still comment on a beehaw post and anyone from lemmy.world or any other instance that hasn't defederates with us would still be able to see and reply to that comment.

Edit: for anyone reading this, the truth is somewhere in between. See the link to the post in the comment below mine to get more clarification.