Theres no going back to Skuldafn as Odahviing said before taking you. You'd have to use PC console commands.
If you are on PC use -
player.additem 00061CA5 1
Too true, there is no going back. Althought if you can ride Dragons there shouldn't be a reason you can't return while flying another one.
I defeated him and took his staff but forgot to take his mask and now it's gone forever since I'm on xbox! Annoying... I have all the other masks. I wish I knew at the time.
thats why you shouldnt be a console peasant
This is why I hate consoles!!!
or maybe, take any items of interest when you are told beforehane YOU CANT COME BACK
also, that was kinda a tactical error on bethesda's part...