There will be no revenge. Instead what will happen is MC's "landlady" who used to be Heras best friend is going to correct Heras course.
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revenge is specifically responding in kind with equal (or escalating) force.
That does not mean the kids won't be avenged. I have no doubt that Hera will be punished in some way, but I doubt that it will be in a manner consistent with revenge, but more in line with "You did bad, do this to make it right and think upon your actions appropriately".
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And with the hints that the crux of the adults plan is up to the MC to resolve, it would not surprise me if Hera becomes a love interest. Probably through a misguided attempt at getting even with her former best friend for "stealing her man" or something similar.
It also wouldn't surprise me if the MC becomes embroiled in the organized crime side of things and replaces Hera (since a woman can't lead the organization per canon) because it turns out the event that ended the "landlady" and Heras friendship is an affair by the "proper" leader making Sky not really the MC's "room mate" and making Aine MC's half-sister.
This would also explain (partially) why Aine had to bully the MC.