Excellent point. Luke knew that fighting wasn't the answer to defeating Palpatine. Maybe Palpatine would kill him, maybe even Vader would die from the wounds Luke gave him, maybe the whole Death Star would be destroyed- Luke didn't care about any of that, he knew his Father was saved and that he wouldn't be corrupted by the Dark Side, nothing else mattered. Even if the Emporer survived the attack, he would no longer have a Skywalker to do his dirty work any more.