Board Thread:Skyrim/@comment-110.33.2.206-20150624062048/@comment-6881629-20150624142918

No you can't go back to Skuldafn on a console or spawn the mask, i don't think he's supposed to be skippable as soon as he spots you he closes the portal and you have to fight him to get the Dragon Priest Staff used as the portal key (another reason to actually fight him as it's kinda unique). They probably just didn't expect people to find a way make it past him so quick.