As we all know, at the end of Diablo 2, Diablo's Soulstone had been destroyed on the Hellforge, and in the preceding cutscene, it showed his soul sort of "dissipating" from his body. My question is, what happened to it? He's obviously coming back in some fashion for 3, but just going off of what was said/shown in 2, it's heavily implied that destroying his soulstone at the Hellforge basically rendered his spirit form impotent and powerless, or even just outright destroyed, depending how one looks at it.
So how, then, is he returning in full force for 3? I tend to think of myself as a lore buff when it comes to the Diablo universe, and as far as I'm aware, there's nothing that explicitly states what exactly happens when their soulstones are destroyed.
Is there a piece of information I'm missing here? Or is it just something that we'll have to wait to see explained in 3?