The angels have left, Satan has won, and everything's over. Not that Sam would know. Sam's buried in his own body, smothered under layers and layers of darkness. He hasn't seen light in years; Lucifer talked to him a lot, let him feel the rumble of death through his own bones. He's killed a lot of people. And for a long time, there's only defeat — no struggle, no relighting of his soul, nothing but surrender. He knows Dean is out there, somewhere, because Lucifer tells him Dean keeps trying to kill him.
It's hard to say what happens, where he wakes up — violently wakes up, like a nightmare hitting a crescendo of screams and motion. It's absurd, really. They wipe out some family hiding out in a half-destroyed apartment complex with a flick of their fingers (well, Sam can only assume; he smells the blood). Lucifer looks down at the speckled red mess and there's toys scattered there, dolls and jacks and a football. There's old, ripped comic books. There are little green plastic men that make Sam/Lucifer's chest stutter. His body feels numb, then cold, then too hot, and Sam pries away at the walls around him, screaming and crying in his own mind. Flashes of memory hit him like punches to his sternum and leave afterimages of Dean — Dean punching him in the face, Dean patting him on the back, Dean clinging onto him for dear life. He couldn't remember the last time he saw him, really saw him, and he remembers Goodbye, Sam.
Sam fights. It's a long, painful fight, and he's caught up in the celestial light of Lucifer, so overpowering that he feels himself being ripped and pulled every which way in the chaos of the struggle. But he doesn't want to go back into the dark. He needs to get out. Needs to fix this, no matter what — he's let him take too much. Even if it inevitably mutilates his spirit, destroys it, makes it tattered waves of energy invisible on the wind, he holds on for dear life and screams with his own mouth for the first time in a long time.
And then Lucifer's grace pours out of him, and light surrounds him for miles in every direction. His soul flutters in exhaustion, rattling and clinging to his lips while the devil dissipates altogether. And then his spirit is nestled again in his heart, or his lungs, or his brain, and it settles miserably there.
Sam wanders blindly, for a few days. While everything starts to fit back into place. He sort of... gets where he is, but it's foggy, and his memory is exhausted from the internal battle. Colors smear and blend, and every so often a wavy smudge that is shaped human runs off, away from him, and he's not completely sure why yet. He's still trying to remember how to walk and move and be a person again; he trips a lot, staining the white pants he's wearing with mud. The coat is eventually discarded, and muscle memory rolls his sleeves in the heat.
He walks and walks, doesn't feel tired, feels like he's slept for lifetimes. He eventually starts recognizing everything: dirt, skin, blood, bruises, corpses. Flowers. Animals and orange-red skylines. They're beautiful. He and Dean used to watch sunsets and stars and things he'd say'd be girly. He... needs to find him. The guy usually gets really anxious when his little brother goes missing, right? They need to be a team again. Sam'll convince him.
Sam staggers toward a meadow, a group of trees. He's sweaty and his hair's disheveled and there's a vacant expression about him, blood dried on his upper lip and chin from his nose. There's a lot being processed right now. He just — needs a minute.
It'll get better when he finds the others.
Everything's fine now.