Quest Oblivion Walker Achievement. HELP

[monsterxbeast]

I'm trying to get all the achievements for skyrim. The only one I have left is the "Oblivion Walker". I need to get all 15 Daedric Artifacts, but I can't get the Skull of Corruption. In the quest "Waking Nightmare", I didn't take it. I tried going back there to see if I could still take it, but it was gone. Then, I tried cutting off the priest's head, and he didn't have it either. I really don't want to start over. I'm level 54, and you have to be at least level 30 to get some of the daedric artifacts.
Is there any way I can get this achievement without starting over?

 

[Squirrel_killer-]

Skyrim:Ill Met By Moonlight - UESPWiki

I you use a glitch detailed there you can get two artifacts from that quest. Otherwise, you have to restart. The staff is destroyed and beyond recovery if you pass it up.