[mooders]

This may sound glib, but have you asked him?

Have you explored with him, with you in a Coaching/Mentoring role, where he sees himself heading; who he sees himself being; what effects he sees himself making over the next year / 2 years / 5 years / at retirement?

Once you have the answers to those (and he may not have fully considered these things himself, to that degree of clarity and detail), you can then work together to see if any options exist where you both get what you want.