Can't grab the Jagged Crown

I've read this on another site:

Upon killing the Draugr Scourge, it is possible that the crown will not be retrievable. The quest icon does not update, and still points to the body of the draugr. Looting the body will not allow to obtain the crown, and the quest cannot continue. If this happens, re-load the most recent save and it should be on the body once killed again.

However it appears you've already tried this (loading before killing and killing again)

I also found this though:

The Crown may be on the floor when entering the room.

So perhaps see if it's on the floor somewhere?

Source: Elder Scrolls Wikia

Open the console and type "player.additem 000DA750 1" (without quotes), thus you will get the crown into your inventory. If the quest still doesn't progress, use the setstage-command; the quest's code is CW02A (Imperial army) or CW02B (Stormcloaks). You might use it more often then, but eventually you'll be able to progress in the civil war quests.