Originally Posted by
Duncanîdaho
One thing with Malthael though is regardless of him taking the mantle of death, he is still one of the archangels. As such, as long as the crystal spire stands, he is immortal. We can kill him, and he will just be reconstructed at the spire just like Tyrael was after being blown up by the world stone. Essentially we cannot kill death without wiping out the entire angel race by destroying the spire.
The only way to actually kill him otherwise would be to imprison his soul in the black soulstone and smash it at the hellforge. We attempted to do it to the prime evils in D2, but the black soulstone snagged their souls once the original stones were destroyed so they did not die.
I think Death is just going to reap the angels for us because we dont have the stomach ourselves to and put them in the stone. Then get us to destroy the stone in hell and end the eternal conflict between angels and demons as he will be sole leader. "Death will have its wings spread over all" will then be fulfilled meaning he will be the leader of heaven and hell officially ending the eternal conflict. The players will then fight at the end of the expansion and kill him(which he wants). By killing him he will be able to reform more powerful then ever at the arch since he is the last archangel. He may become the embodiment of everything since there no one else around to share the powers with (Prime evils and archangels are dead but there places still need to be filled) and become a Anu/Tathamet type of god to set up for 'The End Days' expansion. /end speculation