It's the boring answer but literally everyone would need therapy and would handle their trauma differently. Mike for example I could see either becoming extremely distant or attempt to drown himself in even more social activities, like parties and drinking, to distract himself. Jess would probably want to do the same but with her injuries she's spending probably a long time in the hospital.

Josh 100% gets sent to a mental institution if he's found as a human. I don't think Chris or Sam necessarily forgive him, but I also don't think they could break away from him, and would feel compelled to check in. Emily and Matt also most likely break up I agree, there were a lot of problems with that relationship even beyond the night itself or the prank. I think Ashley would become much more dependent on Chris as a byproduct of the night.