Warning: don't read if you haven't watched the season 6 finale.
This is my take on how things could continue from where season 6 ended. For a while I couldn't think at all and then this idea popped into my head and it made me happy cause it fixes a few things.
Dean could only stare; he didn't know what to say and much less what to do now. He could only stare at Castiel who was looking all high and mighty, waiting for them to bow down in front of them and profess their love onto him. Like that was ever going to happen.
There had been a time when Dean would have done anything for Cas. But not now and not like this. He hardly recognized Cas anymore. This was not the angel whom he had considered his brother and his friend. This was someone who was drunk on power and didn't know himself anymore.
Dean noticed that Bobby and Sam were both looking at him, waiting for a sign from him as to what to do. He shook his head once. They would not bow in front of this creature.
Castiel had noticed this little exchange between the three hunters and he knew what Dean's gesture meant. They would not do what he wanted them to. They never would. Stupid, stubborn little humans. How could they dare? He had just saved them, again. He was the most powerful being they had ever met, their new God.
He sighed and looked down at the floor briefly. There was only one option left now and despite their betrayal and denial it wasn't an easy one. But it had to be done. Castiel snapped his fingers three times in rapid succession and before they knew what was happening, Bobby, Sam and Dean exploded into tiny bloody bits, just like Raphael had done before them. He looked around the room once more and then left to find and destroy all of Raphael's followers.
It took him a few weeks but eventually he found every last one of them. But now that this war was over and all his enemies were gone, Castiel felt suddenly purposeless. He had no idea what to do next and he felt lonely.
Usually he would have gone to talk to Dean in a situation like this, but Dean was gone. He had killed him and all his true friends. Only now did he realize that he might have won the war but that he had lost everything else in the process. Now that he had time to reflect on everything that had happened, everything he had done he felt terrible. His friends had only been worried about him and he regretted how he had thanked them for it.
It was time to somehow set things right now. He had the power to do that and he carefully started working on giving his friends their lives back. He took his time, careful not to make a mistake, like he had with Sam's soul when he'd pulled him out of the cage. He had to do this right. Cas knew that they might never forgive him, but he had to at least try or he would never forgive himself.
When he was certain that everything would work he let the three hunters Bobby, Sam and Dean come back to life in Bobby's living room. He himself did not go there at once. He gave them some time to come to terms with what had happened. Eventually they figured it all out on their own and when they called him he came.
"Hello, Dean." he greeted the hunter, for it had of course been Dean who had called him. "Hello Sam, Bobby." He looked at the three of them, trying to decipher the emotions on their faces, but failing.
"Cas, what the hell happened?" Dean asked after a while and Cas explained everything to them. How he'd been high on the power of the souls, how he hadn't really been himself anymore and killed everyone who had gotten in his way. How he hadn't been able to distinguish between friend and foe. He didn't leave out a thing.
Then he told them how, when everything was over he had realized what he had done and how terribly wrong he had been with a few things.
"I am terribly sorry about those things. I don't know if you can ever forgive me, but I had to at least try to set things right. I couldn't live with myself any longer, knowing what I had done to you." he apologized.
"What about all that juice you're carrying around? Are you going to get rid of it? Because there's no way in hell I'll ever trust you while you're all nuked up like this. The power will just corrupt you again eventually." Dean said after taking everything in.
"I intend to put the souls back to where they rightfully belong. There is just one more thing I need to do before and I could use your help with it. I need to find and eliminate Crowley. He started all this." Cas explained his plan.
Dean nodded. "Getting rid of Crowley sounds good to me. He corrupted you in the first place. All right, I'll help." He looked around at Sam at Bobby, who hesitated for a moment and then nodded. They would help as well.
Dean suddenly stepped forward and hugged Cas who was so surprised that he didn't know how to react. "You're gonna have to earn our trust again, but it's good to have the old Cas back."