Had Obi-wan not allowed Vader to kill him, how long do you think it would've lasted and who've won?

I think that it would have been a stand off. Vader only found it so easy to kill Obi-Wan, because Obi-Wan had baited him into it. He played on Vader's temper to ensure that Vader would become enraged, and kill him without a second thought. Obi-Wan wanted to die so the others could use it as a distraction, and get Luke off the Death Star as fast as they could. So if Obi-Wan did fight him for real, I think one of them would have backed off. That was their second fight in ANH, so I really don't think they longed to fight eachother again. The you should not have come back line kind of speaks of that.