Just realized that if you pickpocket the Mushroom from the Bone Cloaks in Act 1 after you gave it to them to complete the quest, their appearance in Act 3 reflects this and the game treats it as if you never gave it to them in the first place, despite it still offering the quest rewards upon quest completion.
It's the same logic as with the Idol situation. Returning it to the druids or the pedestal should have the same effect as pickpocketing the Mushroom from the Bonecloaks.
Given Larian made a conscious decision to implement this change for pickpocketing the Mushroom for Patch 7 (Or was it 5?), I'd say it makes sense for the Team to apply the same logic to the Idol situation.
