Sprocket, I'm sorry for your loss, on both levels.
Perhaps if you son knows why you left, and that it wasn't because of some action but because of your beliefs, he might be willing to listen. Offer him the chance to show you the light, to refute your beliefs, and perhaps he will take you up and come across some new light himself. Of course, fear may prevent him from doing this - a close friend once told me "I don't want to hear this, stop." when I tried sharing the issues I was personally concerned with.