I want to guess what will happen in the next chapters. As we have already found out from Iwabuchi's words from chapter 74, the goal is to force Soska to have sex with someone. In parallel, he wants to break his heart. The main question is how he is going to break his heart, what should happen?
1. Quite an obvious option, a demonstration on the big screen of a sex video with Rika. But as we realised, it won't be able to break a heart, because Soske already knows that Rika is cheating on him.
2. It's also quite an obvious option, it's that Siho and the unborn child are not from Soska. Most likely, Soska will be ready for this, since he did Siho's DNA test behind the scenes and the manga didn't show it to us.
When Iwabuchi realises that his plan has failed, he will switch to blackmail. Most likely, it will be a choice between publishing Misato's photo and information, and having sex with someone. For Sosuke, it will be a very difficult choice, between his principles and the saviour of Misato. Of course, he will choose to save Misato, but since he has a "problem" he will not be able to do it. Who do you think will come to Soska's aid? There are two options:
1. Satsuki, she will somehow get to the party and try to kill Iwabuchi.
2. Rika, she will be brought by Misato and Akiba, and she realises that she can lose Sosuke forever.
3. Sister Akito, she will decide to sacrifice herself for the sake of other women.
If this is points 1 and 2, then Rika's goal is most likely to prove to Soska that he is not able to save everyone, that there are factors that he cannot influence. Most likely, this is what happened to Rika in the past, when no one could save or help her, which is why she became "what she is". In this case, after the fall of Iwabuchi, Misato and Akiba will not be able to find Rika. Rika will go to the roof to commit suicide. Most likely, the last dialogue between Soske and Rika will take place there. With her suicide, she will again try to prove to Soska that he will not be able to save everyone.
As for point 2, Rika probably realises that her "games" have gone too far and if Soska has sex, he will no longer be the one she loves so much. She realises what a creature (scum) she was in relation to him. And it is her actions that will crush Iwabuchi, she will decide to protect Soska. She will tell Iwabuchi's secrets, and if she has access to the server, she will forgrate it.
What do you think about it?