The base rules state that a Hero's Heroic Feat is "reset" after each encounter. I can find no mention in the RtL rules regarding an "encounter". Can the Heroic Feat be performed once for each Quest, including Side Quests, or only after each Story Quest, or only once once for the entire Campaign?
All rtl quests are one encounter. You can use it once per quest. In the delve you get one reset at the act transition, and the app will tell you.