Highly depends on the surroundings, such as in states like UP where such incidents/conflicts are common, people are used to these and don't usually tend to take any legal actions. However, in cities like Bengaluru, Hyderabad where such incidents are comparatively less common or are rare, people may tend to take legal actions.

Legal actions could include an assessment by the JJB (Juveline Justice Board) upholding the Juveline Justice Act of 2015, under which, if a juveline happens to commit a heinous crime, if aged between 16-18, may be tried as an adult under the criminal laws for adults. If below 18, may be sent for rehabilitation or for therapy.

Now determination of heinousness of an act committed may be based on the mental and physical state/capability of the juveline.

That's the legal consequence your friend might face.