Regarding step 2. This is in Germany so it is very likely there will be people retaliating on behalf of the girl. Boyfriend, brother, father whatever it might be especially since there is a video and especially that most people still hold "you don't hit women values".

Even school principle could easily suspend him for punching a girl and the fact she slapped him first won't really stand up for much. At best they both get suspended. No matter how much people like to see "justice" vast majority of school officials won't see it that way especially over in Europe that's big on traditions.

Either way thank you for taking the time and having a civilized discussion about it. Its okay to have different perspective on things.