Well, “Absence” revealed that Jack killed Mary, and it seems like she might not be coming back.
Supernatural is notorious for killing off its characters and then bringing them back, to the point that one actor was even able to pick his favorite of the many ways his character died.
So, when last week’s episode ended with the implication that Jack had done something awful to Mary after burning off the remnants of his soul and killing Nick, it didn’t necessarily mean that she was dead and gone for good.