Screw Sam and Dean, they probably won't be fast enough! You grab the gun, knowing that you only have seconds. You turn and fire. You weren't prepared for the noise and you drop the gun out of fright. The relatively unscathed demon stabs you through the stomach.
The gunshot brought Dean and Sam running, and you have hazy visions of them battling and killing the demon. Then they rush over to you, but you can tell by the way they are looking at you that you will die. I mean, come on, did you expect anything else? Not really. You WERE fighting a deadly demon, and tried to take it on YOURSELF when experts were just in the next room over. Now that you think about it, that was kind of stupid. Oh well. At least your family's killer is dead. And now you get to join your father, mother and... your sister. Yes, you get to see your sister again. The comforting thought brings a smile to your lips as you fade away.
THE END (And by the way, I DID give you hint about this ending. Look, this is Chapter Thirteen! 13? The unlucky number?)