you can still post to .world, but that post won’t leave your instance if .world is not up to boost it to every other instance subscribed to that community.
if you posted to a .world community from sijw while .world was down, i won’t see it until .world gets back up, gets the message from sijw (which will usually retry a few times before timing out), and boosts it to blahaj. except for cases like this where i’m replying directly to you all 3 instances need to be up for federation to work properly