Ok so I've just completed the murder quest in Windhelm and for some reason the strange amulet I got has not reverted into the Necromancer's Amulet. I did not give it to Calixto unfortunately so does anyone know if there is an alternate way to turn it into the Necromancer's Amulet?

Your boned.

You're boned*
In any case, there doesn't seem like a fix for this short of using console commands or reverting to a previous save. Just one more quest item in your inventory that WILL NEVER LEAVE (doesn't add weight though, so that's not an issue).

Yeah.. unfortunately, I made the same mistake my first playthrough for Blood on the Ice. I was just so happy that I finally got it to fire I ran through it as quickly as I could just to get hjeirm. One thing to remember for the next play through, sell it to Calixto, you'll get it back from him when he.... no longer needs it.

And all this time bethesda has not fixed this issue?!?! WHY?!?!