Sam and Dean have long been retired. Dean and Cas got married years ago, and Sam and Gabriel followed shortly afterwards.
But Sam has felt lost and incomplete for as long as he can remember, as if he has been looking for something that he cannot find.
One day, he is walking quietly along the beach with his dog, his hands in his pockets, the waves just reaching his feet. Suddenly, he feels something nudge up against his foot, deposited on the shore by the waves.
He reaches down to pick up the soft, dark, salty object, and takes some seaweed off of it. As he realizes what it is, he turns it around, staring incredulously. He smiles a little bit.
Sam Winchester’s shoe has returned. He is whole at last.