It's up (and fast) for me rn. They have been getting DDOS'd in a way specifically targeted for sites running Lemmy. Lemmy is still beta software so hopefully this can be a growing experience for the greater Fediverse. The .world admins are some of the most capable out there.
Well, a lot of the communities are hosted on world. I know they make the biggest single contribution to my federation ingress. So, I mean you will kinda notice a bit of a content drought if they're down long enough.
I ended up creating an alt account on lemmy.blahaj.zone because lemmy.tf was down, so now I have two accounts with the same username wirh one as a back up