I want to see an FAQ on this, because to me I see no reason why you can't use Willpower and keep Obi-Wan alive.
Obi-Wan's text doesn't require him to actually BE defeated, it just requires there to be a time BEFORE he is defeated. I would think that you get to use the Second Chance that Maz/Cargo Hold gave him, use the blue card, then check again and if he doesn't have more than 10 damage on him, he's not defeated. This seems to be the only way to justify his ridiculously high cost.