Dean was back in his hotel room in 2009 and he had just said no to Zachariah. By now, the other angels had probably received word and would be coming up with some crazy plan to get Dean to say yes; something that would put Sam at risk because that was the easiest way to get to Dean. But what they didn't know, was that Dean knew there was a way to stop the apocalypse, he wouldn't have to say yes to Michael and Sam wouldn't have to say yes to Lucifer. It was simple logistically. Just a gun and a bullet and the world would be saved. He didn't know how he would have the strength to do something so evil. Is it evil though? Is trading one life, albeit the most important life to Dean, for the billions of lives around the world evil? Could Dean live with himself if he went through with this plan? He didn't know for sure but the more he thought about it the more he didn't think he could. There was no other choice though. Dean was resolved in this decision even if it killed him- the only sure way to stop the apocalypse was to kill Sam and burn his body so he couldn't be brought back. No Sam, no vessel for Lucifer.
Dean called Sam and set up a meeting by a river in the middle of nowhere. He needed to make sure there were no witnesses for what he was about to do. Dean framed their meeting as wanting to possibly start hunting together again so, of course, Sam was ready to meet as soon as possible. Dean pulled up to their meeting spot. It was still dark out, but Dean was sure it was early in the morning. The sun would be rising soon. He pulled his revolver out of the glove box of the Impala and made sure it was loaded and ready. Sam's car pulled up just as Dean got out of the Impala and hid the revolver under his shirt. Dean needed to do this fast so he wouldn't chicken out. No talking, just pull out the gun, point it at his brother, and shoot.
Dean was facing the driver side of Sam's car, waiting for him to get out. His hand was on the revolver, his adrenaline racing, heart pounding. He was as ready as he'd ever be. He just hoped Bobby could forgive him someday but he knew that wasn't likely. Bobby was good at holding grudges. Sam got out of the car and started walking toward Dean. Before he could think too much about it, Dean pulled out the gun and pointed it at Sam's head. He pulled the trigger and Sam fell to the ground. Dean stood in the same position for a minute. He was in shock. He really killed his brother that he had dedicated his life to protecting. He didn't need to go over and look, he knew Sam was dead. He also knew he needed to burn Sam's body but the longer he stood there, the more guilty he found himself feeling until the impact of what he had done finally hit him. He fell to the ground in absolute despair. He had done a lot of horrible things in his life but this really took the cake. He thought again about what Bobby would think of him now, what his father would say, the way his mother's heart would be shattered. He couldn't live with this. He took the revolver and put the end of it against his temple. He was started to pull the trigger-
The gun was gone. Dean was confused. He had pulled the trigger so he should be dead. Maybe he was dead and that's why the gun disappeared? But he still felt awful and he could still see the outline of his brother's dead body in the light of the rising sun. Then, Sam's body also disappeared. Now Dean was really confused. He got up from the ground. He looked around and when he turned he saw Zachariah. Again.
"Hello Dean," said Zachariah, cheerily. This made Dean feel enraged. He went to punch Zachariah but he had disappeared just as Dean swung.
"You son of a bitch! I just went through hell in 2014, seeing my brother as Lucifer's meat suit. I ended his life to stop the apocalypse! What did you do with his body?!"
Zachariah responded, "this isn't real either Dean. Sam is still alive and well. You didn't seem to get the message when I sent you to the future so I thought showing you how much worse the present could be might make things clear. Remember this immense guilt you feel from killing your brother. Both of you saying yes and following your destiny is better than this, isn't it?"
Dean thought for a second. He hated to admit it but he thought Zachariah might have a point. He didn't want to say yes to Michael, and he still intended to find a way out of the Winchesters' horrible fate, but for now, he could see Zachariah's point. Before Dean could respond, he was suddenly on the side of a road with Cass.
"Good timing Cass."
"We had an appointment," said the angel, looking very proud of himself considering he typically didn't show much emotion other than anger.
Dean put his hand on his arm and said, "don't ever change." Dean knew what he needed to do now. He needed to get back together with Sam, but for real this time. He wouldn't kill Sam but he understood that it was better for them to be together than apart. He had hope, just a little bit, that together they could find a way to stop the apocalypse and avoid saying yes to Lucifer and Michael.