::: spoiler spoiler
I broke into Wyrm's Rock and assaulted Gortash at his coronation, where Wyll's dad, Lord Ravenguard, was present. I won the fight by falling back to the parapets (by the ballista) and forcing all the enemies to walk through Hunger of Hadar and Wall of Fire to get to me; they really hate pathing through Hunger of Hadar, so most of them waited politely in the main room while I killed the rest a couple at a time.
I knocked out Ravenguard and then shoved him to a safe place so that he wouldn't get hit by any AOEs. However, now that we're done, the post-fight cutscenes are over, etc., he's still just KO'd. Wyll doesn't have anything to say about him, and the quest journal entry about rescuing him is still on the step where it says that he's being held at Wyrm's Rock. Well, yes, I know, I found him.
So what do I do with him now? He's infected, it doesn't seem like I should wander off without him. I tried going to camp and there's still no quest update or word from Wyll. I tried healing him in case we need to talk to him, but I learned that KO'd characters don't get up when healed.
Update: If I long rest, the journal updates to say he is dead and his body disappears. It also implies the existence of a next quest step at camp, but Wyll says nothing about it. Also all my companions had the wrong dialog after a certain camp event, as though I had not yet killed Gortash who is very dead. Curiouser and curiouser. I think it's definitely true that they didn't plan for you to try to use the nonlethal toggle this way.
Interesting! In Early Access NPCs could definitely wake up from nonlethal damage, because in my EA save file I knocked out those adventurers at the abandoned temple near Emerald Grove, and they kept showing up again with 1hp so that I could gently boop them unconscious again. ^_^