IIRC the content is on multiple. If there's a single user on lemmy.world subscribing to content from somewhere.else's foo community, then foo will be synced to lemmy.world and if somewhere.else is taken down it will remain on lemmy.world.
But someone correct me if I'm wrong.
Also, it isn't just about servers going offline. If a single server does something bad, you can just switch to a different one and enjoy the same content you've been seeing.
I'm just going to start not answering the phone unless it's a number in my contacts. If it's important they can leave me a message.