This is assuming he gets out of that alive. First public humiliation, then death. Or imprisonment or enslavement with a lock on his ability. But just letting him go free after that, or with any capacity to charm his way out of captivity? That would be dumb.
Well the author already showed us a VERY dumb part in the story.
The girl the mc already freed from Sain's brainwashing tried to kill herself at least once.
Trauma strong enough to make you want to end yourself won't go away just because "someone talked you out of it one time", all the things she has endured remain in her head and the memories will just gnaw at her mind all the time, especially when she is alone, and that will inevitably lead to her relapse, leaving her alone and is the single dumbest thing one can do. And that's one of the reasons I don't have much faith that the author will do the right thing and have Sain put to death (at best I can see Sain being turned into a monster and the MC being forced to kill him, but that's equally as weak and dumb plot).
Also the fact that the MC whose main trait is that he is full of hate because he was betrayed by the people he trusted most, decides to "ease up" on his hatred, because he learned that it was not all of his friends and lover betraying him, but rather his oldest friend that raped them...don't tell me that's a reasonable/non-dumb character development now...any normal person would want to murder him on the spot especially after seeing how much he messed up that one girl's mind.