By 'second film', I actually meant 'any further films'. The inclusion of Father Skywalker in Brackett's ESB obviously contradicts the end product, Father Vader couldn't crop up later in this storyline, which I think it's best to treat as a dead end. That's my position on it. While SW was being shot, Father Vader still didn't exist, even as a vague notion in the back of GL's mind (although it's possible to theorise about what led to him making the decision). The volcano duel storyline came about from the notion of Vader being a walking iron lung, which was developed in audio post-production with the breathing effect. It's my belief that Father Vader occurred to GL when he began picturing the volcano duel, which originally began with Father Skywalker being killed. GL then took one more step, and Father Vader was born as an alternative, although he was still committed to following the orthodox Father Skywalker storyline at that point, hence the existence of the incompatible Brackett draft (& whatever material GL developed for it).