There is only one scepter to retrieve. If you bail out before you get it you could go in again.In the throne room do you have to get the 2 chests with the goblin king's scepter, or do you only need to get 1 chest? , I took a chest, I ended up leaving the place because I was attacked by the elite goblins, the mission was not complete, when I went back there, the chests are empty, and I only have 1 scepter
Thinking of it, if you bail out there might be the issue that Gwynn won't give you another invisibility potion.
Impossible to get without the potion past the initial guard, so you might want to backtrack.