Yesterday, the developers of Garry’s Mod, the 2006 Source engine sandbox game, announced on Steam that due to a takedown request from Nintendo, they were removing all the Steam Workshop (i.e; user-generated) content that used Nintendo’s IP. Some originally believed that this was a troll of some sort posing as Nintendo, but this screenshot tweet from Garry Newman, the titular developer of Garry’s Mod, indicates that he’s certain the takedown request is legitimate, and the probably-still-ongoing removal of Nintendo content on the workshop will continue.
The Nintendo Network service, that handled online play for the vast majority of 3DS and Wii U games, Splatoon included, was shut down on the 8th of April. So yes, the official servers for Splatoon are dead.