It would be easy.
Sam could relax his arm, let the jaws come at him.
It would be quick. The werewolf is strong. Its fangs gnash, saliva drips, muscles strain, all to sate an insatiable hunger. It has teeth that will tear through Sam's throat in moments.
He'll be dead.
But 'keep fighting', Dean had said. He'd made Sam promise.
Sam gathers his strength, throws the beast off. He rolls out of the way before it can regroup, scrambles to his feet.
"I can't do it without you," he says.
The werewolf gives him a quizzical glance.
"I don't want to."
The wolf hits him, the momentum carrying them both to the ground. Sharp silver cuts through cloth, skin, muscle. The creature grunts, writhes. Its final breath huffs, hot, over Sam's cheek.
"Please don't leave me," he whispers. He shoves the dead werewolf off, the blade still embedded in its heart.
Dean is gone. Sam is alive. Maybe it's time to call Jody. If Sam doesn't come back from a hunt, someone should know about it.
Worse than feeling Dean's last breath leave him, would be being stuck on earth as a ghost, never reaching his brother in heaven.