Maybe not outright destroy Darrel, but it would be cool to see that kind of a "lose to win" ending. Ethan asks Nat to move away with him to another city (due to a lucrative job offer, or whatever), which means they (she) would have to leave Darrel behind. After Nat talks to Darrel (during which they have sex for the last time), she agrees - and the two of you move away. Ethan looks happy, finally getting rid of Darrel's influence in their life, and we flash forward a month later: Nat tells Ethan she is pregnant... and that it's Darrel's baby.