With this guy it seems more likely to me that he has no idea how to teach
drawing, and arrogance is often a cover for incompetence. Have you seen his
work? It wouldn't surprise me if he also didn't know how to draw.
Or, he may be ok and just be scared silly.
It may be that the input (hey - you're ruining the art program) needs to
come from the administration and the parents of your former students. Let
them put the pressure on, and let him know you are available for mentoring -
but make Him come to YOU. But he has to make his own mistakes. It's always
painful to watch a job you made something special be reduced or destroyed by
whoever comes after (personal experience).