http://wikipewt4n75trifcse2ggaieot27svognl7idu6xmmqn37kf64rvsyd.onion/index.php?title=Main_Page
In addition to an onion simply being gone (Tor cannot resolve the onion), sites that display 404 (and use a known onion/URL based hosting service) are the only other thing that is considered truly DOWN. Presumably the account is gone. If a service has been down for a while, tag it with ' - DOWN YYYY-MM-DD' (your guess as to when it went down).