Honest question back - if he is already committed, why would he not be able to be the leader his HS team most likely needs him to be? Surely there is plenty of time around even the "extra" HS season to be involved in continued competitive travel org play.
Even then, as a HS coach, I would welcome, encourage, allow those top players to participate with their travel orgs during our summer season if that was their preference. It usually worked out best for all involved - gave others in the HS program more opportunity to show themselves and gave the top players continued play against top level competition. I say this with the caveat that numbers can often be an issue for some programs.
FWIW, we have had many players come through our HS program and go on to successful college (and beyond) careers. VERY few have not made every effort to be leaders by being there for their HS teammates whenever possible and, in fact, tended to be the ones leading out with extra or voluntary small group practices. Again, communication and advanced planning were always key to manage specific travel org events. That combined with the above-and-beyond commitment and leadership with the HS program went a long way toward alleviating any conflict.