In the years following Inarius and Lilith secretly created Sanctuary in the name of the Nephalem which is the child of angel and man, the council of Archangels met to decide humanity's fate. Tyrael cast the final vote, and this means that he's responsible for that decision by others in the Angiris Council, leading to being mortal prior to Diablo IV Gold. Diablo 4 all for the good of mankind. His role in the forthcoming game isn't yet known, but there are some probable ways in which this character might be a factor in the future of the series.
Diablo 3 explores the depths of Tyrael's tale, as he turns into"the" Fallen Star by tearing off his wings and crashing to Sanctuary to where his descendants from the Nephalem are residing. When he is joined by a powerful descendant, Tyrael is able to eliminate the Prime Evils and takes charge of his Black Soulstone. The moment the Archangel of Death, Maltheal, went after the stone and began to attack his companions He was the one who brought his partner to Pandemonium to destroy death itself.
Tyrael decides to remain in his mortal body, but then reconnects with his angelic friends to become both The Aspect Justice and of Wisdom. Diablo 3 ends with him considering whether his new mortal counterpart, who is likely to become corrupted should one day become the next menace towards Heaven, Hell, and Sanctuary or even life itself. Aspect of Justice and Wisdom Aspect of Justice and Wisdom likely won't sit idly by as 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 is a scene of Inarius fighting Lilith with armies at both their backs. Although the scene doesn't show Tyrael's direct involvement, his invention of Horadrim as well as his influence on the Paladins of Sanctuary means he is surely at work. Light and dark battle in the battle, and now-dead Tyrael is somewhere in between.
It is possible that his presence will be experienced through these intermediaries unless events force his hand. Tyrael is still feeling the effects of destroying the Worldstone at the conclusion in Diablo 2. The mystical artifact shielded Sanctuary from Heaven and buy Diablo IV Gold Hell and now is the protector of the land in its stead. Tyrael does not appear likely to lead any further ventures into Hell or venture much further in to the Pandemonium Fortress, where he might offer advice similar to Deckard Cain for those who are willing to listen.