Sam Winchester is not afraid of Hell. He's been, and saw, and conquered. Hell is backing Lilith up against a great stone dais, with blood on the floor. It's throwing the Devil into the ground. It's waiting for fire to sear its song around him; it's waiting for Abaddon to peter out. He's not afraid of Hell or any of its knights, or kings, or fathers. He hands Dean a small cup of something sweetly caffeinated, and the mark is there but old. Dean thanks him.
Sam knows that if he loses his brother, he'll be losing Dean to Dean.