His agreement with Rika was that he could do anything with Sousuke. That's her condition in exchange for inviting Sousuke to the Orgia party. Considering the end result, as she said, was going to be the same, then it makes sense she does not care how Iwabuchi treats Sousuke. As Miyabi told us that Iwabuchi has favoritism towards Momonga, it complys without problems.After chapter 92, I think I'm starting to see Iwabuchi's tendencies and goals.
1. As we know, Iwabuchi likes seeing others fall into despair.
2. Besides that, he seems to always want to control the people around him. So he prefers using sex as bait for other people rather than using it for himself.
3. I'm a bit unsure, but it seems he's also quite rational when it comes to money and benefit.
Then what I can conclude:
1. We know he made an agreement with Rika that he could do whatever he wants to her. So what I initially thought, that Iwabuchi wanted sex with Rika seems to be wrong. Iwabuchi wants to use Rika for some bigger purpose, like drawing in more influential people such as politicians, journalists, and so on.
2. Given the tendency that he's probably rational about money or benefit, I think what will happen in the next chapter is that Sousuke will try to make an offer too. He'll try with money first, but Iwabuchi will refuse him, or because Sousuke is dumb... I mean, naive. He'll realize the money he has won't be enough. Then he'll try to offer something that Iwabuchi won't be able to refuse...
I believe conclusion 2 is more in line with the characters so far. Though, Sousuke's bid could be something as ludicrous as divorce, or even some joke fto stall for more time, which ends with Satsuki arriving.