Normal
First off, does the bottle have only water? If not, you'll need to start diluting down any juice to help protect his teeth from decay. The next step would be to help him become attached to something else that will comfort him to sleep, like a stuffed animal or blanket. The problem is that you may not want to put too much energy into this. As you said, he will give it up when he's ready. Kids on the autistic spectrum often lag behind in developing self-soothing skills.