I don't recall them ever showing what happens when a Godtier is "killed" but doesn't die. If you've got an idea as to how to handle that, that's all I need to know. Doing the Windy Thing is something he'd be able to do, but whether he'd remember how to do it is up to you.

He would have his own sylladex, but you'd have to request it if you wanted to play with a new one/spread it around the game. As for the actual contents, I'm trying to remember what John had last. Things like his Dad's hat are fine, SBURB constructs like the item creators, the salamanders and the Tumor aren't. Really, as long as you don't use it to bring in tons of Homestuck stuff without going through item request, I'm happy.