Caleb is kind of an unhinged monster, wouldn't count him out of doing something final. Quinn's family/friends too... while not involved in a DIKs party, Maya's father is a control freak psycho, let's not forget Josy's own brother, Tommy, or Bella's ex being somewhere, either for real or in her head, Jill's family or Tybalt, and Quinn's presence in Sage life...
I mean, don't know if you played Acting Lessons (I suppose so), there's already an Ana (Zoey), multiple 'Angela/Hedwig' (HOTs and other inconsequential flings), Liam (Derek), so, to me, there's no way there's not a Leah somewhere, and it most definitely won't be an obvious one (like... Bella... I'm kinda scared of what's hidden behind that locked door).
And like you said, that ending may affect a lot of people negatively, and it won't be because it sucks (100% sure of that)