First things first, the main girls are clearly defined from the beginning. One can argue that Quinn is the side girl with the most content and importance to the plot, which I agree on. I sometimes wonder if the author is not regretful of not having made her a MG, considering that he seems to keep a special place for her. But in the end, she remains being a side girl.
Now, as for what will happen when Maya finds out about Quinn and the MC, well, it depends: firstly, discovering what exactly. Because it is not the same if Maya knows about Quinn and Fuckface having sex once or more times as if she discovers that the two of them are getting closer by the day (if their relationship continues to grow).
And it also depends on Maya's and the MC's relation at the moment of truth. If he is together with her and Josy, and they then discover that he fucked Quinn is one horrific scenario for the MC. If they are just friends, they can get upset by that or very upset in the case that things with Quinn are getting more serious.
Many possibilities, actually. We'll see for sure. Popcorn time, anyway.
I am not sure how dark the doc is willing to go. Having one of the main girls in some kind of corruption path looks a bit too much, perhaps. But I am not sure either. In any case, if such event happens, I'd expect for three conditions to meet at the same time: the MC having DIK affinity, a good relationship with Quinn and the worst possible one with Maya.