According to Iger, 4 people made the decision to diverge from Lucas's outline: Alan Horn, JJ Abrams, Kathleen Keneddy, and himself. Whoever proposed the idea, ultimately Iger assented to it, though if he was the only one of the four of them who disagreed it would not have gone forward. Ultimately Iger is to blame for deviating from Lucas's story. It's said a lot that "the buck" stops with KK. But that's not completely true, since even she ultimately reported back to Alan Horn and Bob Iger, who if they wanted something for Star Wars (such as a hectic release schedule, and who knows what else) she had no choice but to follow it. Their role in the destruction of Star Wars is too often understated.