"This is a tough one."
It is not a tough call. It is his responsibility to go. That is what being a monarch-in-training is about.
There is a phrase that has no meaning in the republican United States, but must be followed in a monarchy, even a limited, constitutional monarchy: noblesse oblige -- the obligations of the nobility. That means that you have to go where the bullets are flying, and put yourself next to the commons of your realm.
I am not a big fan of hereditary government -- in whatever fashion the term is cloaked. (Look at my handle. Read the poem on my freep page.) If a nation has a monarchy, then its leaders must step up to their responsibilities -- as Prince Harry has -- or be prepared to abdicate. Harry, his father (who served in the Royal Navy during a time of peace) his uncle Andrew (helicopter pilot in the Falklands War), his grandmother (served as a woman volunteer in WWII), are the reasons why the Brits still have a monarchy.