I would absolutely let him go - it might be the hardest thing you’ve done as a parent, but it will be so worth it for his education and emotional growth.
I had the opportunity to do a rotary exchange, and I can’t remember why I didn’t end up doing it - I still regret not going to this day. We hosted about ten different exchange students (not through Rotary, though) over the course of my high school and college years, and my parents continued hosting exchange students until my youngest sibling left home two years ago. It was a wonderful experience for us.
I don’t know about being an exchange student, but of my siblings who were at home during the host years, every one of us has lived abroad for at least two years, visiting our exchange students’ families and experiencing other cultures like they inspired us to do. If you end up being the host family in return, it will change your children’s lives. We all consider ourselves citizens of the world - we live anywhere, but are always happy to return home. It does make my parents a little lonely now that they have an empty nest and three of their four children regularly out of the country.
I’ve been in Korea for five years. My younger brother dated a German girl that he met in our exchange program. They broke up amicably, and her family invited him to live with them for a year as he was doing an apprenticeship. Then he lived for three months in Oman in the middle east as well. My sister also went to Germany, Italy, and Costa Rica, spending about two years in Germany, six months in Italy, and three in Costa Rica. Friends call us the “international family”. We all speak between two and four languages. We are all confident and react well to uncertainty. We have all had interesting opportunities in our lives, educations, and careers because of the international experiences we’ve had growing up and living overseas. I highly recommend it.