Diablo 3 ends with Diablo IV Gold him contemplating whether his new mortal counterpart, who is likely to become corrupted should someday become the new danger towards Heaven, Hell, and Sanctuary, or even life itself. There's a reason that Aspect of Justice and Wisdom will not be able to sit back while Inarius is a mighty army that marches through Hell in search of his past love, Lilith.
The most recent Diablo 4 cinematic trailer from Blizzard features Inarius looking down Lilith as well as armies at both their backs. While the scene does not mention Tyrael's personal involvement, his creation of the Horadrim and his involvement with the various Paladins of Sanctuary suggests that he's in the game. Dark and light battles on the battlefield, and the now-dead Tyrael sits somewhere in between.
It is likely that his presence will be felt through these intermediaries until events require his intervention. Tyrael is still feeling the effects of the destruction of his Worldstone at the end in Diablo 2. That mystical artifact protected Sanctuary from Heaven and Hell and now protects the region in its place. Tyrael appears unlikely to lead any further charges to Hell or travel any further than what is known as the Pandemonium Fortress, where he may offer advice like Deckard Cain for those who are willing to listen.
Five playable Diablo classes have been released so far and all are variants of earlier games. Given each installment so far has provided something different and exciting, maybe Tyrael could become an active participant in the fight, balancing the sides by providing players with the ability to summon angelic or demon powers to perform duties to Sanctuary. This kind of system is likely to be similar to the multi-tree development that was confirmed for the series.
It's doubtful that Blizzard intends to turn Angels as well as Demons into classes, considering that the franchise focuses on the people stuck between them. But as a mortal stuck between Heaven and Hell, Tyrael sits in a position unlike any other in the entire Diablo legends. It is likely that he will be an equalizer in the tale, perhaps even the voice of reason instead of being a party player like he did in the past. Although he may be forced to take sides, Tyrael is now aware of the true value of the mortals, which is the way he is likely to take part in the events of cheap Diablo IV Gold.
