Given there's only so many events in a school year to cover, I wonder if the author will run the gamut of "school-coded youth events" for them to experience together, and then end it there with the final chapter being Mizuno seeing Wakao's face.
I guess non-school things could be covered as well (they did do a convenience store chapter), so that would mean stuff like Karaoke and Summer Festival (other big "milestone" events, to be sure), but my guess is if Mizuno ever does end up seeing her actual face, it'll signal the end of the series.