We already had Zenos killed, had him revived and had some dark entity take his body. If it happens again there just wont be any poing in his arc. Especially if he starts helping us and will be our buddy/scion. Just as senseless as resurrecting Hades/Hyth.

No matter how much Zenos helped us he still did horrible stuff in the past, and turning everything upside down and throwing away that he almost killed our friends and tortured ppl will be just plain dumb.

Remember the whole Tsuyu plot and the Role quests for ranged classes to see how those "redemtion arcs" can look from the side.