I feel bad for Jimmy.
Sure, he had prayed for this, asking for years to be of use to the Lord. He was a devout and good man, but he still had a family who he loved and cherished.
Poor Jimmy had never imagined everything that would happen to him, or that he would end up being killed thanks to his request.
Now he was in heaven, at long last, and Castiel could continue using his true vessel without interrupting Jimmy's life indefinitely, but it still didn't make it better, not entirely at least.
Jimmy would have lived a good, long life if he hadn't claimed possession over his body.
When he first arrived on earth, the truth was he didn't even consider feeling guilty or bad about any of it.
Now, though, after everything he had gone through, Castiel was experiencing emotions he wouldn't have even understood before.
Poor Jimmy, he thought to himself, as he stared at the vessel's reflection in the mirror. His body, in many ways, even if it wasn't his own entirely.
He had lived so many adventures in it, though...
When he returned to heaven, he decided, he'd apologize to poor Jimmy. It was the least he could do.