If he comes back, it will ruin the whole story, and the idea that our guardian is slowly drifting to the darkness. If they bring him back, then there’s willl be no story for Uldren. We wouldn’t still hate him, because there would be no need to.
Oh dang, that actually sounds like a pretty good storyline you got there, how our guardian is slowly drifting to the darkness, how cool would it be in the joker's wild DLC our guardian does something really messed up like killing a bunch of innocents just to complete a mission, and then from that moment forward they start to have a darkness effect on them, like what Uldren had in his eyes during the Forsaken campaign, and by the time Destiny 3 rolls around our guardian has turned to the darkness.
That sounds like a pretty lit character arc to me.