John isn't in hell any more. After he escaped the hell gate to help save the crew, he disappeared into a bright light. They can't find him in heaven, I remember, so I think he ended up in purgatory. I also believe Mary is in purgatory. She didn't sell her soul; as it was said, she sold what turned out to be Sam. Even so, making deals with demons isn't likely to get you straight to heaven.
I finally was able to start watching this show in the new year. It was fantastic, but I felt it wouldn't be interesting for long if it was simply a monster-hunting show. Thankfully, that wasn't the case. From season one, each season, and sometimes a series of seasons, had an overarching theme, or mission, or what have you. I finally caught up this morning, watching season 6 ep 15, and watching ep 16 after having put it on DVR. Season 6 started really, really weak to me, and it wasn't flowing in the least. I think they've finally got it on track, but I think it really took them half of the season to do so.
I'm worried, too, that in recent seasons through the present they've been killing off characters at an alarming rate. The one big mistake they made, I think, was choosing Lisa over Ellen and Mary Joe. I really couldn't stand the whole drama early in Season 6 with the 'will they or won't they stay together' with Dean, Lisa and Ben. Way, way too soap opera for me. For my money, they should have only killed off Ellen, and had Mary Joe be Dean's love interest. That way he could have stayed in the game, had his girl to take care of him in his grief, and they wouldn't have to have met Sam and his new crew.
Overall, however, this show is absolutely fantastic. I have loved every season but season 6, and even that season has finally come around. I really hope it keeps on going with quality seasons, since I was so late to the game