Note: Keep in mind that in end!verse, 'Dark Side of the Moon' never happened, so Dean doesn't actually know what heaven is like.
"Don't make me do this, Sammy." Dean's voice is barely audible, but it doesn't waver. His eyes are set, his back is straight, and although he doesn't want to do this - wants nothing more than to not have to do this - he will, because he needs to. If he needs to. Until that is proven, he'll try his best to get out of it.
"How many times do I have to tell you, Dean?" It was Sam's voice that spoke, Sam's lips that turned up in a smile as he laughed, Sam's body that moved ever so slightly closer to Dean; but this wasn't Sam. "Little Sammy doesn't live here anymore."
"Bullshit," Dean spat, shaking his head at Lucifer. "He's in there somewhere. I know you can hear me, Sam."
The most sadistic of smiles crept onto Sam's lips as his body took another few steps closer. Dean didn't back away, didn't even flinch, as Satan himself drew near, stopping less than a foot in front of the Colt, which Dean held in outstretched hand in front of him. "You're right, you know," Lucifer whispered, Sam's hazel eyes sparkling as though he were telling Dean the juiciest of secrets. "He's in here," he tapped a finger just above his right ear, "screaming and kicking and fighting to get out. Still, after all these years." Dean's eyes narrowed. He knew Lucifer was just trying to get to him, to shake him, but he wanted so badly to believe Sam really was still alive in there.
"Don't worry, Sam," Dean called, voice still surprisingly level for the amount of distress he felt. "I'm gonna kill this son of a bitch, and you'll be free. You can go to heaven, where you belong." His voice cracked then, and Lucifer laughed.
"You really think my vessel is going to get into heaven?" he asked, amused. "Do you even think heaven still exists? My brothers have long since deserted your kind, Dean. Heaven isn't-"
"Don't listen to him, Sam," Dean interrupted, speaking through clenched teeth. He tightened his grip on the gun in his hand. "You'll get into heaven. You'll get to meet mom. You can drive Baby all the time, and not have to deal with me singing."
"You really think that's how heaven works?" Lucifer asked, but Dean ignored him and continued on.
"I know you hated my singing. God, I sucked, didn't I?" Dean let out a laugh, shaking his head slightly at the memories. "You'll get to see Jess again. Maybe in heaven you'll wake up next to Jess and you'll get to go to that interview, you'll get to propose to her, live happily ever after." A single tear slid down Dean's cheek as he silently prayed his words were true, although it killed him to think that what he was describing would really be Sam's vision of heaven. "Maybe in heaven you'll get to live your apple pie life for the rest of eternity, and your life with me will just be a bad dream. A distant nightmare."
Lucifer's face had been blank as Dean spoke but now he looked down, took an unsteady step backward, shook his head. Dean wasn't sure what was going on, but he hoped to God - if God was still out there - that maybe Sam was fighting his way out. Hoping against hope, he continued.
"Maybe you can have kids in heaven. A dog. A nice house with a big, fenced in yard. And listen to your douchey music all you want." Dean laughed shakily, a last attempt at holding back the rest of his tears. "Have a real Christmas. One that doesn't involve stolen presents and decorations. One that isn't a last ditch effort to distract yourself from your screwup brother getting ready to go to hell."
"Dean," Sam's voice gasped, and Dean faltered, because this wasn't just Lucifer through the filter of Sam's vocal chords. This was really, truly Sam. He looked up at Dean through messy bangs that had fallen out of place while Lucifer shook his head, one hand clutching at his temple, and his eyes looking so pained and confused that Dean couldn't stop himself from dropping the colt at his feet.
"Sammy?" Dean asked breathlessly, and almost instantaneously Sam was rushing forward, throwing his arms around Dean and pulling him into the tightest hug Dean had ever been a part of. And Dean held onto Sam like his life depended on it, digging his fingers hard into Sam's shoulders, reaching up to run a hand through Sam's hair and pull his big baby brother's head down, holding it in the crook of his neck. He buried his face in Sam's hair and let the tears fall, all the tears he'd stockpiled over the past five years of facing the apocalypse with some semblance of a smile on his face. He felt Sam crying too, felt the silent tears against his neck as they clung helplessly to each other, stayed like that for so long neither of them was entirely sure it was still the same day of the week when they finally pulled apart.
"Man, I've missed you," Sam said, the saddest smile Dean had ever seen pulling at his lips. And as much as he wanted to reciprocate the sentiment, Dean took a step back from Sam, took a deep breath to calm himself, and asked the question that needed to be asked.
"Is he still in there?" Dean's face was set in stone. There was still the possibility that this was a trick to get him to let his guard down. He hadn't come this far, survived this long, just to fall for the most obvious trick in the book.
"I.. I don't know." Sam looked down at the ground around him for a few moments, then clenched his eyes shut and concentrated as best he could. "I can't feel him, but I don't know where he would have gone." He opened his eyes again, looked up to meet Dean's. "I might have shoved him back into the little corner he had me shoved in."
"How do I know for sure?" Dean asked, taking another step back, holding eye contact with Sam as he knelt down, picked up the colt, straightened himself. He kept the gun down at his side, but his fingers tightened around the handle.
Sam laughed. A hollow, breathless laugh, but a laugh nonetheless. "He thought what you were saying about heaven was what I really wanted. He didn't know why I was fighting, why I didn't just want you to kill me and get it over with." Sam took a few steps forward. "I sort of caught him off guard. I think that's why I was able to get out."
"Why did you claw your way out, then?" Dean held his ground, but watched Sam warily as he approached. He still looked so lost, almost pathetic, after years of being ridden by the devil. Sam just shook his head, disbelieving smile on his lips, and closed the distance between himself and Dean, leaning down to press his lips against his brother's.
It had been over half a decade since Dean had felt those lips on his, but they were exactly as he remembered. Just as soft, just as loving, just as welcoming; and when Sam hesitantly ran his tongue over Dean's bottom lip, and Dean obliged the silent request and parted his lips, he was amazed to find that Sam even tasted like himself still. All the memories of all the kisses before came flooding back to him - from quick, hurried kisses, ducked down in the backseat of the car while John was in the store buying them chips and soda for lunch, to long, slow, loving kisses in locked hotel rooms when they were finally alone, to deeper, passionate kisses shared when they were older and shared their bodies with each other as well - but the one kiss that really jumped to the forefront of Dean's mind was the most important kiss that never happened. When he and Sam had parted ways all those years ago, they were so hurt and angry with each other that they never got in a goodbye kiss before Sam left.
And now, with that in mind, Dean gripped his hands in Sam's floppy hair, completely unraveled from the nicely styled 'do Lucifer had worn, and pulled him in close, losing himself in the familiar taste and smell and feel of his brother, because there was still a damn good chance that this would be their last kiss, and if it was then Dean wanted it to last. But then, when did Dean ever get what he wanted?
When his hands went up to tangle in Sam's hair Dean had haphazardly dropped the colt again, but this time Sam caught it. Only it wasn't Sam anymore. He pressed the barrel of the gun against Dean's chest as he pulled away from the kiss, and when they parted Dean's stomach dropped. His hair was back in place, his back straight, and his eyes were cold. The only emotion on his face was amusement, thinly masking ruthlessness. Dean took a few steps back in shock, but he knew running was no use now.
"Sorry, Dean," Lucifer said with a wicked grin, sounding as though he'd just won some sort of prize.
He has, Dean thought to himself as his eyes trailed down to the Colt in the devil's hand. He just won the earth.
Lucifer cocked the gun, teasingly softened his smile, and said, "I guess your baby brother is still your weak spot."
And then the world went black.