To me, this is much ado about nothing. Kids have always cheated. In my time, students reworded what they read, but they still used what they read instead of their own words. The internet has allowed copy/paste as well as the complete sharing of work, so this took a turn to more overt methods, but the old school method was cheating, too.
To be honest, almost none of the subject matter plagarized is going to make the slightest difference in the long term development of a high school kid. Teachers would like to believe that everything that we teach our children is essential, but that isn't even close to true.
The only real question to me is whether this kid has shown himself to be a cheater across subjects. If so, he will learn the hard way that life doesn't allow for this after school. In the real world, we sink or swim on our merits, not those of others. People who don't learn to work hard early usually suffer in life.
So, who cares about whether or not he gets to stay in the NHS. I was in the NHS through school. It was never taken into account when I chose my school, and has never been taken into account since. I knew it was just an empty organization then, and it still is today. I didn't do a thing to try to "earn" being in the NHS - never gave it a thought.