So yeah, I wouldn’t be surprised if the season ended with Mary making a similar decision as Gavin in this week’s episode. Her being back also kind of “upset the scale”. Who knows all the things that may happen still in this season, how many people may die in the crossfire. I could definitely imagine the show to tie all the arcs up with explaining it all - maybe even Lucifer having a child - with Mary dying again could undo this timeline (you know the whole thing of “never being born is different to being killed” approach). And we’d get some sort of goodbye scene like these above in which Mary reunites with John like Gavin and Fiona did.