She was resurrected by Darkness in the finale of season 11, only to be stuck in an alternate dimension with none other than Lucifer himself, only a year later. Mary Winchester, in the finale of season 12, was among other stars of the "Supernatural" cast that had to sacrifice themselves for the greater good. The fandom was not happy when Castiel had to die, Crowley had to die for good, and when the Nephilim Jack was born; however, about Mary's fate, the fans have contrasting opinions about if she should come back or not.
Where is Mary?
Despite the controversy, it has been confirmed by the show runners themselves, such as Andrew Dabb, that Mary Winchester is very much alive in the alternate dimension where she is stuck.
Mary will have a story line of her own in season 13, which will represent the journey of how she will manage to survive with Lucifer following her every step, and in a world where every being is out to get her. The alternate dimension that represented how Earth would be if the Winchesters had never been born, will be explored in some episodes of the upcoming season 13. Andrew Dabb also announced that Mary will explore that new realm and make friends with new characters.
How will this affect the brothers?
What will differentiate Sam and Dean Winchester in this season, will be their attitude towards Jack, and the presumed death of Mary Winchester. Sam will have a more compassionate approach towards Jack since he has faith in the fact that he might very well turn out not to be evil after all.
He will try to relate to him due to his past when his demon powers were active. However, Dean will be much more hostile throughout the season, since he also blames the creature for the trapping of Mary in the alternate dimension, and the death of the beloved Castiel. Dean will be very secure of the fact that Mary Winchester is definitely gone and she will not come back; however, Sam does not share this opinion.
He will try to convince Jack throughout the season to re-open the portal to the other dimension, in order for there to be a chance for Mary to survive and return to the family. Since Dean disagrees with this attitude, this will cause a lot of continuous bickering between the brothers.
Both the Winchester brothers will be devastated about the loss of such an intrinsic part of their family, their mother whom they were finally getting to know, and their extended angelic family, Castiel. Although Mary Winchester has not been very anticipated by the fans throughout the season, she will always be a Winchester and we are happy that she is still kicking.
