I can reach it just fine. Maybe you need to flush your cache / DNS?
Generally speaking though, unless they have provided alternative means of contact and you saved them prior to the outage, there’s nothing you can do. Same if they decide to shut down - the instance and your account would be lost, and that’s that.
Edit: you can look up the owner of the domain on sites like https://who.is, but more often than not they use anonymizer services to not reveal their residential address. The given email address there might however serve as a forwarder to their actual one.
All of them. I’m browsing /all simply to block more, so that they won’t accidentally show in my feed.