Deckard Cain - new Archangel of Wisdom and successor to Malthael? He just has to tell Tyrael to stop crying and go back to justice.
Maybe we go to Pandemonium to look for Leah's soul. Imperius is against it because he hates us, boss fight!
But wait, there's lore! Malthael appears, lore happens, boss fight!
Then we find Shen's gem, Dirgest appears out of nowhere and another boss fight!