I don't know the exact wording, because my computer won't let me get on the reg! But anyways David's Harp's ability is something like "Return a Hero that is being discarded during battle back to the top of your draw pile."
Say I make a RA, and my opponent blocks with Emp. Galba "Each opponent must discard a card from hand." If I choose to discard a Hero from hand, can I instead put them on top of my draw pile? I would guess yes, because it fullfills David's Harp's ability (A Hero discarded during battle)