Finding out what happened to Grunaxe is a quest which, having seen his ghost, I think you have completed. I believe you will get credit for it just by letting the NPCs blather on once they give you that quest (think it was the warriors guild).
The only thing you can do for the unfortunate Boogres is leave access to the idol of Aku open so they can touch it and be restored. They won't though. Would have been a nice addition to the game if you could have really helped them.
Wyv
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