The banker certainly wins the bet in terms of the money that he put up. Because the lawyer left the house before the 15 years were up, he loses and the banker keeps his money.
I'd say the banker wins in other ways too. He learns something about himself, which is always good. He may not like himself much t the moment the story ends, but he can get over that, I think.
It's pretty hard to argue that the lawyer wins. He doesn't get the money. He ends up miserable. Hard to see how he won unless you're going to say that having this new knowledge of what the world is like constitutes winning.
im trying to figure it out