Well whether it is bad narrative or not and yeah I agree even if she would there should be some hell to pay with various girls for sure and not a quick acceptance by all considering the intentional hurtful mean actions she displays.
If she does not end it herself though and it is only MC saving the day, then she will just be to dangerous for them to keep around, bound or not since someone always can escape especially with Eris being able to take over Scarlet whenever she wants to set her free. So either Sarah frees herself from Eris's influence and grows up or you have no choice story wise to kill her.
It's very unlikely that Sarah dies.
First, killing a character is extremely rare in porn games. It's not GTA
Second it would be a waste of asset, given the time spent designing her
Third, why would Haichi have Sonya move her like that if not to give her an opening ?
Last, once Eris is neutralized, she'll be a perfect sex slave for a few years before she has earned back her freedom.
But that's just me of course
