nd almost practically ensures that the three Prime Evils are stuck in the Netherworld.
Oh, no it doesn't. Now that the Worldstone is destroyed, there's nothing to seperate the worlds anymore. Before, the angels and demons could only come in/on to Sanctuary as mere ghosts of what they really are. Remember The Sin War? It was raging all around us humans, but we never saw it. The worldstone made it seperate from Sanctuary. Now that it's gone, angels and demons alike can come on to Sanctuary in their full form, not just shadows of what they are, which is the case in the game. That means that if the Prime Evils find a way onto the Material Plane, they will be far more powerful than ever before. Sanctuary can survive without the Worldstone, but it's far more vulnerable now. It may take many heroes to save the world if the Evils get loose again.

And I only mentioned the books because Knaak wrote most of them. They're rather good, and if he's working on the storyline for a possible D3, then it will be good. Knaak has experience.