PeterKahlke

You were right, of course. I wanted so much to believe, but... sigh.

What makes you say that?

With both Michael and Lucifer showing up, I can think of one way to at least give Sam and Dean a fighting chance...

My guess is that God will be weakened from the battle with Jack, which will even out the power levels.

I'm 99% convinced that since they revealed it so early (basically at the end of last season, with Death confronting Jack), the plan for Jack to kill God will fail, probably in ep. 15.18. In ep. 15.19, it will be Sam and Dean versus God, and there's only one way that can happen that fits with what we know about this season, with the last four seasons, and with the whole mythology - and that's both Winchesters saying yes to Lucifer and Michael, and using their powers to beat God. It's the only way to properly end it.

With Mary, we might not notice the difference.

I think if the dead do come back en masse, it'll more likely be due to the last angels dying and heaven falling, or Jack killing Chuck.

NEXT ON SUPERNATURAL Sam and Dean search for the yellow-eyed thing that killed their mom.

"Wherever it's darkest. Wherever he is." - Nick. So Lucifer comes back tonight.

Not that I recall, but last season spent a lot of time developing their relationship. Mary may have faded into the background since, but she was a mother figure and only friend to Jack when he was fighting the war in apocalypse world. She's in a few consecutive episodes later this season (which in itself is a bad sign - look what happened to Charlie), so that would be enough to remind viewers of their bond.

Judging by the conversations Jack's had with Cas and others, his story going forward seems to be about far he'll go to protect the ones he loves. His (near) soullessness won't make him "go dark side", but rather make him impervious to the morality of his actions. Theory: Mary dies, Jack tries to resurrects her and fails, driving him towards anger/frustration. Applying the WWWD advice, he does something monumentally stupid to bring her back. He'll believe the only way to protect/bring back the people he loves is to get more powerful. As the snake in the story kept consuming eggs until it killed him, Jack will look for more and more archangel grace to consume, regardless of the consequences. He either opens the cage to get Michael's grace (the "old fan favorite") or teams up with Nick to bring back Lucifer somehow, to get back his original grace - or both. Which of course all ends well.