I'm so sorry about your friend's accident.
That's great you are in touch with his family. Maybe you could send a card with a photo or flowers and let the family know you are there waiting to be contacted? If you call once in a while for news they are likely to pass on to your friend news about the phone call and eventually he will probably ask to see you.
I think you are right about not wanting to overwhelm him right now. If you speak to him, keep the conversation simple and don't change topics rapidly!
If you guys hit it off great once, you are likely to again... I can understand your fears about how things will be different for him and the two of you after the accident... I would give him time and be patient and follow his lead to see where he is in the healing process.
I wish you both the best of luck and to your friend a speedy recovery!