Hi mlj
I have been thinking about your situation for several days and I certainly think you shouldn't give up on your friend keeping the door open will provide a means of escape if he does come to his senses. We all would like to think we would never be taken in so easily, but in reality the JW faith is very crafty they catch people when they are at a low point and get them hooked over time.
If your friend won't talk to you I suggest you write to him and explain how hurt you were by what he said at your last conversation and that this has created a very negative impression of this new faith of his. Surely if he has found such a wonderful new way of life he would have wanted to share what he was learning with you.
JWs are taught to share their beliefs and not to create a bad impression or reproach on the JW faith. If you can phrase it right you should be able to get him to agree to talk to you. If you ask him to share what he has been learning he will probably think he has a possible new convert, however, if you keep your wits you can use this opportunity to find out what has been going on. If he does agree to talk or to your visit try to make sure he doesn't bring other JWs into the discussion as you just want a private talk with him.
Be aware you may not be able to get him out of becoming a JW, but at least you might be able to come to some understanding and let him know that you will always be his friend and that you are there for him whatever happens.
I hope this is helpful.