M.P.
I would change him. The most important thing is that he will be familiar with her, and there will be kids there that he knows. If that is the best place for him then you move him. I bet you he will transition easier than you think he will. As long as you do not make a big deal (in a negative way) about it, then he won't. You need to approach it with excitement, and tell him who of his friends will be there, and Mrs. So&So....etc.....You could even take him to visit for a bit so that he will be a little bit familiar with it before he starts attending. I personally would go with the director, if she is as great as you say she is, she has left for a good reason, and she may not be at liberty to say what that reason is......