Tyrael is able to keep his mortal form Diablo IV Gold, but joins his angelic brethren and becomes both his Aspect Justice as well as of Wisdom. Diablo 3 ends with him considering whether his new mortal companion, who might be corruptedin the future, will one day become the new challenge of Heaven, Hell, and Sanctuary as well as the very existence of life itself. The Aspect of Justice and Wisdom likely won't sit idly by as Inarius marches an army upon Hell in search of his first love, Lilith.
The most recent Diablo 4 cinematic trailer from Blizzard has Inarius confronting Lilith with armies on both of their backs. While this scene lacks Tyrael's personal involvement, his contribution to the Horadrim and his involvement with the various Paladins of Sanctuary ensures that he's in the game. Light and dark battle across the field, and now-mortal Tyrael is a middleman.
It is possible that his presence will be detected through these intermediaries, unless circumstances force his hand. Tyrael is still feeling the effects of destroying his Worldstone at the conclusion of Diablo 2. This mystical object protected Sanctuary from Heaven and Hell, and he acts as the protector of the land as its successor. Tyrael does not appear likely to lead any further steps to Hell or travel any further that his current position at the Pandemonium Fortress, where he may provide advice like Deckard Cain for people who remain and listen.
Five Diablo playable classes are currently being announced and all of them are takes on options from earlier games. Each installment has provided something different Perhaps Tyrael will be a part of the battle to balance the two sides by offering players the opportunity to be transformed into angels or demonic powers , in exchange for responsibilities to Sanctuary buy Diablo 4 Gold. This kind of concept could very easily build on the multi-tree expansion that was previously made public for the series.