Dean is fifty-eight.
He's started to slow down from age and injury. This time the werewolf is just a little too fast for him, manages to give him a fatal bite before Dean plants a bullet between it's eyes.
Dean lies there in the filthy alleyway, slowly bleeding out though he saw at least one person peek out their curtains earlier in the fight. He curses the fact that he sent Sammy away on another hunt, a salt and burn a few towns over. He was so confidant in his abilities that he didn't think he needed back up for a simple werewolf hunt.
Dean closes his eyes for a long moment. When he opens them again a familiar looking old man is standing over him.
"Hey." He says, not quite managing a smile.
"Hello." Death replies.
He leans down and grabs Dean's arm like he's going to help him to his feet but instead Dean feels a drifting sensation. Dean struggles.
"Your brother is safe tonight. Let go, Winchester." Death says and Dean does.
He lets it all go and drifts off into peaceful oblivian.
"Goodbye, Dean Winchester." Death says as he spreads his wings and takes off, carrying his precious bundle cradled in both hands.