Fine let's break it down to pieces.
Sage: "The thought is nice, but could you imagine a party with DIKs and alphas?"
Sage: "And I don't mean like our party with just MC and Jacob; I mean a full-scale party with everyone."
At this point Sage is not serious about having such a party. It's a joke.
Riona: "That would be a disaster! They're hardwired to hate each other."
Riona joins in on joking about it.
MC: "Yeah. Even if one or two of us might get along, there are too many of us that never would."
MC: "Like, imagine if Dawe and Tommy had to party with each other. I’d give that party two minutes before it went south."
MC joins in too. They are all joking about a hypothetical disaster party.
Sage: "I think you’re being too narrow-minded on that one. Imagine if the party was huge, bigger than this one."
Sage: "Do you think it wouldn't work when there are that many guests? The DlKs and the alphas wouldn’t even have to talk."
Sage starts to play devil's advocate. She is beginning to warm up to the idea.
MC: "Maybe at first, but you know how alcohol brings out the worst in some? I just don’t see it happening."
MC responds semi-seriously. He agrees that having a lot of people might help, but it would only delay the inevitable.
Sage: "Well, you'll have to think about something. I doubt we’ll be able to fool the alphas easily after this."
The idea has been put on the shelf, but it is no longer just a joke.
Next day the HOTs are helping the DIKs clean up and alphas come to complain. Now Sage has to start mediating between them for real. Two months of frustrating talks later Sage is ready to make that joke into reality.
It's how narrative foreshadowing works. Because the characters joked about how a party with both DIKs and alphas would be a disaster, there is going to be such a party and it will be a disaster.