Eh, I don't think anything will happen. Shiina got into a bad mindset and if there was to be any actual assault aside from desperate "pindown" it would happen now, and not have a "cliffhanger" of this sort.
While of course, this isn't good, I gotta say this is a really neat story. To show how society can pressure you into certain things that affect you even when you're "Not entirely" as the society would like you to be. However odd that phrasing sounds. Even if you just look at it from an age gap perspective, worrying over those things isn't that odd. Although, as I said before, I think there's a lot more pressure on poor Shiina. While it doesn't make what she's doing justifiable, I still don't think it'll be an actual assault.
Also, I just noticed but this scene here is how this entire manga started huh.
And I have to say that after that last scene, the trivia page seemed a bit comical in terms of timing. "Anyway, that sexual assault attempt aside, here's some trivia about this place they had their first date."
I actually once thought that the first scene was from the time when Shiina was drunk, but if you look closely, she's not wearing the same clothes as when she went out to the bar.
I also appreciate how the manga goes into how Shiina feels pressured to get into a relationship, and to a lesser extent, how her sense of inadequacy is worsened by how Takagi, a woman 10 years her junior, seems to be better at her job. The final chapter seems to indicate that while Shiina's a bit sad that she and Takagai can't get married, she's more at ease about her current state. Besides, the fact that she and Takagai catch the bouquet indicate that they might get married soon.
In all fairness to Shiina, while she is desperate, I don't think she'd go so far as to even attempt sexual assault. Once she comes to her senses, she's overwhelmed with remorse.
As for the trivia, that's one reason why the date and the meeting with Takagai's ex should have been in a separate chapter, and then there could have been a half-chapter worth of buildup before this cliffhanger.