Alright, okay, let's do a thought experiment. Just a little what-if, entertaining the most unlikely scenario. Let's assume Nakatani Nio loses her mind or some pushy Editor says "We need to stretch this out at all costs, so we can have a second anime season!" or something like that.
A possible way to drag out the plot that is not completely outrageous could be that Sayaka confesses during the school trip, but, now hear me out, Touko is in a pretty confused and depressed state. She can't make head or tails of her situation. If Sayaka confesses and Touko asks since when she has been hiding this and Sayaka says for a while or whatever, then Touko will see it as an echo of how she hurt Yuu. But unlike Yuu, Sayaka is not afraid to face her and even says she will accept a rejection.
Now Touko always appreciated how Sayaka doesn't pressure her and let her keep secrets, but she also realizes that Sayaka actually saw through her. Sayaka knows that Touko is changing and would actively support this. Where Sayaka keeps a strong front and keeps pushing, Yuu retreated out of consideration and denial.
In this scenario there is a possibility that Touko might accept the proposal of going out with Sayaka, to see where she really stands. She is close to Sayaka, but didn't tie her down like she did Yuu. She might not feel romantically for her (yet), but she wants to know if this current her can actually even feel like that anyway. Sayaka's love is passive, but straightforward, unlike Yuu's which has been painful and indecisive.
Now, obviously I am not saying this would lead to a Touko x Sayaka endgame. That is literally impossible for this story and I won't play devil's advocate for that. Still, if they started dating for these improper reasons, it will lead to Touko slowly realizing that it is different from what she feels for Yuu and that the love of a partner is not harmful. Yuu will obviously get hurt in the process from seeing that and has to deal with shutting her feelings down harder than before, but now that she actually knows what love feels like, she also feels heartbreak all the more. Jealousy and all those emotions she never had.
Ultimately it will end with Sayaka giving Touko the push to ask Yuu for forgiveness and mend their relationship, because she is sympathetic like that and doesn't want to live a farce.
I think this kind of arc is not unfeasible, but still highly unlikely.
PS: Don't make fanfiction of this, even Nakatani Nio can barely make this work. lol