John Doom said:

Frank your Majesty said:

To conquer isn't to kill, so I guess Luke wanted to defeat the Emperor in another way, maybe with the help of his father?

Well, by "defeating" I didn't necessarily mean killing, but throwing away your lightsaber isn't the smartest idea against that guy, either :D

Obviously, it was succesful ;)

Luke: "I'll never turn to the Dark Side. You've failed, your highness. I am a Jedi, like my father before me"

That is his success, his plan to turn Vader worked out, even at the last moment.