All that remains is to deliver the Crown of Will to Sharlindra in the Undercity. She will see that it is delivered to Lady Sylvanas. I would warn you against thinking to use it for your own purposes, <name>, Mug'Thol's fate should be illustration enough.
So this is the relic the ogre used to duck the will of the Dark Lady...
Strange that something so simple could wield so great a power. And to fall into as clumsy hands as those. Well done, <name>, I will deliver the crown to Lady Sylvanas, and see that she hears of your accomplishment.