Honestly, all Sou has to do to be allowed back to school is get mad, but he's too nice for that.
Sensei is an opportunist. I do feel like it's kinda on her to thoughtlessly approve of the class exchange like that. Ironically, this probably wouldn't have happened if she bothered actually paying attention to the crazy things Sou was doing instead of just reducing him to a bonus.
Erika-sensei didn't really do anything wrong. She's supposed to educate her students, sure, but they were all well-behaved girls that nobody was expecting to make contact with an SCP.
....I also don't approve of this "Konno Sisters" narrative of shared responsibility. Just what did Aya do? Hana was the one who started all this.