So play as Uldyssian? Or as another mortal-Nephalem who helped assisted Uldyssian as an unsung hero?
Either way, it would be interesting.
That said, while the heroes of Diablo 1 were corrupted by evil, the same can’t be said of the Diablo 2 heroes, as for the ones that we know of, they hadn’t been corrupted.
Sorceress Isendra - Took in Li-Ming (D3 Wizard) as a disciple, until she was murdered by an assassin sent by Valthek.
Amazon Cassia - Returned to Skovos Isles to further train her people in preparations of the coming evil (According to HoTS).
Necromancer Xul - Took up an apprentice, Mehtan (and Lethes according to Diablo Immortal).
So once again, for the most part, the Diablo 2 heroes had seemingly avoided the corruption that the Diablo 1 heroes had suffered from.
Now as for the fate of the Diablo 3 heroes, as you said, we may have to wait for Diablo 4, before we see as to whether they have perished, suffered imprisionment, became corrupted, and/or still out there weakened but still fighting against the darkness.
Anyway, I would like to play as Uldyssian. But as the character has been designated as male, probably playing a hero acting as his confidant would make more sense. This way, we can play either gender, and the game could weave a new perspective on the conflict.
Like, the hero would open the narrative: “Let me tell you a story about Uldyssian and the Sin War.”
The bittersweet ending of the story would make a great closing despite a lot of people already know how the story would end.