At this point I don't see it as a means of adding to a happy ending. When replying to some else it hit me with how the talk could possibly go.
As I've said, I've basically come to terms with Sakura not facing any sort of punishment for sleeping with Fuckboi. With 2 chapters left I just don't think there's time for it.
The two may very well meet. Ideally, next chapter. Mio and Sakura see Shinobu. And the two talk. Nothing is brought up. Nothing about Shinobu's innocence. Nada. Maybe how fuckboi told Shinobu that he had sex with Sakura, which may further strengthen her resolve and cut ties with fuckboi further.
Ideally, she tells him she's going back to doing guavure work. It seems like she's made the realization that that's what she wants to do because of the fun she's had with it. Mio is there to support her. Shinobu sees this and trusts Mio. Knowing Sakura is in good hands, he'll support her. Ending things on good terms.
Then we cut to Fumi. The talk strengthening Shinobu's resolve. Vowing Fumi that he will support and protect her while she also wants to support him. Bringing them closer together. Hence, the two being together with Shinobu and Sakura being on good terms.
If I had to condense everything to try and salvage what I can for this manga. That's probably how I'd do it. This likely means no sex scene unless there's an epilogue chapter but.. that's one direction I could see this going. But that's if it happens. This could very well be wrong lol