"I am become Death, the destroyer of worlds," -J. Robert Oppenheimer
...
In the silence of the End, the disquieting nothing of everything falling apart, they will always be there.
These are the secrets they have kept as the keys to the undefined and the unimaginable. These are the days of darkness in the light of normality, the days of lucid dreams and nightmares that wake. These are their days, and theirs alone. Without one, there is no other. They are as connected as the skin is seamless, as flawed as the stars and the seas. But they are blood, and they will not forget that.
Friends have come and gone with them. Some have died, buried nameless in fields unknown. Some have become what they fear, monsters in the mind and dead in the heart. And some are there but never there, lost deep in the catacombs of insanity. They remember the ones they've lost. Write their names in memories and locked rooms.
But they will always be. Two by two, marching to death as the day wears thin. Drive the roads alone, and fear nothing. Saving people, hunting things. For the family. For themselves. For dirty diners and good music and a car that never stops, for the fire that wrecks and the fire that heals, and the burned-down house where a great man once lived. For the fallen and the returned. For that Heaven that was and the Hell that never should have been.
For everything.
They will always be, these Winchesters.
Together in life, together in death.
Without one, there is no other.
Sam and Dean will always be.
Or else the End will finally become them.