In my campaign, one of my players used a wish granted to him from a god to get forgiveness from someone he had killed who had become a revenant. I really didn't want to say he can't so I'm trying to figure out now what happens with the Revenant.
What happens to a Revenant that can't(or won't) complete its task?
Best Answer
The lore on 5e Revenants is pretty limited, being pretty much just the 3 paragraphs in their Monster Manual entry, which makes it hard to tell. We essentially have 2 things in there to work with, namely:
and:
These two things suggest that a Revenant unable to exact revenge (because it does not want to avenge anything anymore) might crumble to dust, and that a Wish spell is specifically capable of sending one to the afterlife (although in the entry, only when it's bodyless)
So probably, the Wish will make the Revenant move on to the afterlife and not bother the PC.
That said; your player just spent a (potentially) incredibly powerful story reward to make an entirely character-story driven choice. Given that the character was not even aware that the person whose forgiveness they asked turned into a Revenant, just silently making the creature not show up as a result of this Wish sounds like a huge disservice both to the cool story of how the person they killed came back for vengeance and the cool resolution of how divine forgiveness ended the Revenant's tormented existence.
As a fellow DM, I think you owe it to your player and your party to ignore what the rules might say and have the Revenant show up in person to accept the player's forgiveness, before crumbling to dust and moving on to the afterlife. This is a story worth sharing with your players. It'll end up much more memorable than not ever meeting a Revenant at all.