That song is pretty rough (I had to look up the lyrics, never listened to him really).
I think a "mental break" ending is possible, but it would have to fit the character and reason it. I am not big on revenge in this story (though act 3 is pushing my buttons) as up until now, Lacey has always been... questionable in motive, but never nailed down as specifically an intent of such hateful motive and disregard for the MC.
A "break" ending where something crazy happens is reasonable though, where he runs off the cliff so to speak mentally, but I seriously doubt the professor is going to allow his favored characters to be "put to the axe" so to speak. Heck, I even think the MC getting any sort of self empowered ending is likely off the tables due to what we have seen so far...
At best, we can hope for an ending where the MC isn't completely left in the dark as it concerns the "happy" of that ending, but still comes up short. It is very possible what the professor terms as "good" could end up making many of us want to throw up.
Now most of the other NTR games I have played out there, honestly... they need revenge endings, and they need seriously punishing ones. The women in those games are evil to the core.
Considering their are only two 'good' endings and one of them is supposed to be a sort of 'love' ending where they end up exclusive, I wouldn't say it would be throw up worthy, it could be a bit of a downer because all those girls that got romantically invested in the MC will have to be effectively friendzoned.
The other is liable to be the 'Big Family' ending aka Harem, where every girls the MC chose to go for will form a big family with him and Lacey, I doubt their will be anything negative about that one, so I assume we are pretty safe on the notion the good endings are going to be alright.
I still support the notion the two neutral endings are liable to be based on the two Act 1 paths other then 'No Fun', I think one will be based on the 'Slut' path and will effectively as you said a ending based on Lacey's theorized goals of making the MC willing to accept her doing sexual stuff with other men to make him jealous so he'll hard fuck her afterward, a cycle of Lacey acting like a slut and the MC reclaiming her.
The other based on the 'Punishment' path I still believe is based on BDSM with the MC being the dom to Lacey's sub, where he control her sexuality for his satisfaction, be her King, but realistically Lacey is effectively in charge but let the MC decide who she has sex with so he can have the illusion of control. So the two neutral paths I expect to be NTS.
So yea I think the really bad is going to be reserved for you know... the two bad and the one horrific ending. A Romeo & Juliette ending where they both die I expect their is a fairly high chance of being there as a bad ending where the MC leave and jump down the cliff and Lacey follow along out of grief to have driven him to that. I mean sure the Prof would hate that, but they'll probably throw it in for those that refused to listen to the repeated warning that separating them would be problematic.
As for other bad ending, its so difficult to say, I thought it could be one where the MC leave with one or more girls going along with him, supporting him so he doesn't end up dead, as for Lacey, I think she'd likely kill herself off, its implied she considered the years in College worst than her childhood because the MC wasn't around, so while it could be possible that she'd return to be like was in College to escape her loss, she'd likely die young one way or another.
And the horrific ending, I would really see this as being a sort of based on the War of the Roses movie, basically they live together but hate each others, she return to her College style slutting it all out, while the MC would be perpetually angry at her and just focus on his other girls, they'd have a very toxic relationship without love where they try to perpetually make each others miserable, but unable to leave one another due to their codependency.