Jack smiles at Dean's question like he'd been expecting it. "He's with me. In Heaven. He's... done, I think. He played a part in saving the world, and now... he wants to rest. I think he deserves that."
Simultaneously, the news breaks Dean's heart and heals it. But more than anything, it gives him something to think about.
His brother looks at him like he has a million times - with an expression that says he knows exactly what Dean's going to say before the words even leave his mouth. "Are you sure?"
Nodding with a gallic shrug, he slides his hands in his pockets. "Listen, man. We've been through it, I mean really through it the last fifteen years. Monsters, gods, cosmic douchebags... Hitler, for god's sake. You name it, we've beat it. And now Jack, he's... he's better. He's better than Chuck, and I'm alright with that. You've got Eileen here, the baby. You guys are good. Everyone's good. But me?"
Sam tries to cut him off, but Dean's been trying to get these words out his entire life, and he's not gonna let Sam stop him now. "Just wait. I'm not happy here, Sammy. I can't be, not with... not with Cas somewhere else. He's it for me, man. He's everything, and if I gotta let go of this life to go find him, then..." He shrugs again as the faces of all the people he loves flash through his mind. "Then I'm good with that. I've lived a lot of lives, man. More than anyone, probably, if we consider that fiasco at Mystery Spot. And I wanna be done. I wanna be happy. I wanna finally look Cas in those stupid blue eyes and tell him I love him too. So... I asked Jack if he'll let me in up there. Say sayonara to this place and just... be."
Dean was prepared for a lot of reactions from Sam, but happiness wasn't one of them. Tears shine in his brother's eyes as he steps forward and pulls Dean into a hug. "I'm proud of you, Dean. I'm gonna miss you, but... this isn't the end. I'll see you again soon."
With a sad smile, Dean pats his brother's back and steps away. "Yeah, but maybe not too soon, okay? Have a few more kids. Train the next generation of Men of Letters right. And for the love of god, burn every copy of Supernatural you ever find."
Sam laughs, but before he can say anything else, Jack appears. "Are you ready?"
"Yeah, let me just..." Dean pulls off his flannel and sets it in the box he's kept Cas' trenchcoat in. "Alright. Beam me up, Scotty."
"Bye, Dean." Sam sniffles, pulling the box close to his chest. "Tell Cas I said I'm sorry it took you so long to admit it."
With a last grin and a middle finger, Dean disappears from the Earth.
Heaven is a lot brighter than Dean remembers it, but maybe that's just because his human eyes were limited. Things look great, and Jack looks around proudly as he leads Dean to the garden. "I no longer keep people confined to their personal heavens. You'll be free to roam, free to see everyone you've ever loved that's up here. I think Cas is visiting with my mom right now."
"Does he... does he know I'm comin'?"
Jack nods. "Yes, he's been watching over you. He's eager to see you again."
Butterflies scatter throughout Dean's stomach as he rounds the corner. He sees Kelly, but she's not talking to Cas, she's talking to some huge, multi-headed thing. "What the..."
"Oh, you haven't seen his true form yet, have you?" Jack asks. "That's what he really is. What he really looks like. Don't worry, he can take any visage he wants up here, so he'll be able to speak with you the way he always has."
As they approach, Dean gets a good look. His wings are wider than anything he's ever seen, all jet black with streaks of blue and green. They're gorgeous, and would've stolen the show entirely if it weren't for the heads. One moose, one squirrel, one insect-lookin' thing that might be a bee... and an Impala. Dean's breath catches in his throat as tears flood his eyes. "Has he always looked like that?"
"No. But you changed him, Dean. More completely than I think you'll ever know. Now... go. I think you've wasted enough time."
As he nears Cas, all four heads turn to look at him. It's overwhelming, but Dean isn't afraid. This is Cas, the love of his life. "Heya, Cas. Long time no see. I uhh... guess I've got some things to tell you. Can you... I dunno, maybe come down here?"
With an almost blinding flash, the giant form shrinks down until he's once again the blue-eyed, trenchcoated angel that Dean fell in love with. He takes two steps forward with joy etched in his features, and reaches out for his hand. "Hello, Dean. Walk with me."