The internet’s best resources are almost universally volunteer run and donation based, like Wikipedia and The Internet Archive. Every time a great resource is accidentally created by a for-profit company, it is eventually destroyed, like Flickr and Google Reader. Reddit could be what Usenet was supposed to be, a hub of internet-wide discussion on every topic imaginable, if it wasn’t also a private company forced to come up with a credible plan to make hosting discussions sound in any way like a profitable venture.
I am under the impression that the info you posted is shared to other server and thus also exist somewhere else. It make sense that your login or handle is gone, but the communities/posts are also gone? There should be some cached content on other server as well. (say if I sub technology at beehaw, it has to send info in batch to lemmy.ca so when I read I am reading from the local cached version instead of pulling data from beehaw directly.)
Also, any serious enough instance would likely have regular back ups and multiple admins to prevent that.
I honestly don’t know for sure. Maybe it’s cached on whatever instance your using, or maybe your instance is pulling the content directly from the target instance’s database (or more likely an API-like ActivityPub request).
I was under the impression that lemmy/fediverse essentially functions like email. Your messages and content are stored on your server, but you can communicate with anyone on other servers.