I’m sorry it took me 6 years to answer you anon. That’s my perfect ending:
They have to die. I want it to happen on a “traditional job”. Not trying to save the world, or because they are Heaven’s weapons to fight Hell. Not because of any destiny crap, not because they’re vessels, not because of something bigger than themselves. It is an ordinary hunt, a vengeful spirit, a wendigo, pick one, a creature just edgy and smart enough to get to them the one second they’re not paying attention. That’s all it takes really, because no matter what their names are, no matter who they are, when the sun goes down they are just bones and skin, blood and a heart beating. They are two men. Who they are, their strength, their courage, the story they leave behind, it’s got nothing to do with muscles, it’s a story about feelings, not about bodies.
And no one is safe from making a mistake, because it is a human thing to do. And that’s what they always have been. Despite the demon blood, despite demons, angels, despite the possessions, sacrifices, rituals and all those supernatural things they’ve seen and been and done. Humans. And that’s why they die, just die, without artifice, without any big and fancy explosion, without saving a world that will never know their names.
And that’s life, as it should be. Maybe their death is the only thing they get to really live.And it’s not like in the movies, there’s no big declaration of love, they just close their eyes and let the darkness envelop everything. Maybe Sam goes first, Dean doesn’t notice at first, because he’s staring at the blood flowing from his stomach and he panics, trying to find the wound to stop the blood, all the blood, too much blood. And when he turns his head to ask for help, “Sam” is a cry that never leaves his lips because Sam is there, stretched on his back, his head turned towards Dean but his eyes already closed and a small smile playing on his lips. And Dean stops fighting. Because that’s it, his job’s over. Take care of Sam. Sam doesn’t need to be taken care of anymore. And what’s even the point of living if Sam is not there to make his life a perfect mess? They have already tried to live without the other, and have already seen and experienced these long days without meaning. No. This time, it’s not worth fighting, this time, everything will be fine.
So Dean closes his eyes and isn’t scared, because he knows that wherever he goes, Sam is already there, waiting for him.