Obi Wan is gung-ho on killing Vader throughout the entire trilogy. Especially in this movie, where he says the Emperor has already won since Luke won’t kill his own father. He seems to imply that was always the plan for Luke, too. Which means Vader’s line suggesting that Obi-Wan once told him to run away together contradicts itself within its own film. So I seriously hope this line is amended. Even ignoring the prequels, it makes zero sense based on what we know about the characters.