you know what? When Mary said, "I'm the only one who needs to be ruined", and her face at the end, I concluded she only wanted to the ruin route because she and Addie could marry.
The nobles would not look at Addie as a marriage candidate since he is just a servant, but looking at all their interactions, I seriously think Mary and Addie likes each other (if it's not too obvious already) but does not want to say anything because of the difference in status.
Therefore! Mary will face "ruin", go to the north with Addie (OF COURSE ADDIE WILL FOLLOW HER), and live a happy life together.