Something that is hard to learn, and easy to forget. When we ask a question and do not receive the knowledge we wanted, one or both of two things happened. We phrased the question in confusing or unclear manner, or we asked the wrong person. I'd say its a bit of both. No one is really sure what you are asking, and ultimately your attorney is going to have to guide you on this.
Put in your contract that if any of those things happen, the clients will automatically be transferred to you. The problem is that the carrier will most likely assign them as orphans to others before you get any of that taken care of. I guess you would call it a risk you will have to take in your situation. I would definitely have a preset price you will pay for the entire book before you get started and a unilateral option NOT to buy the book. In other words, he is under contract to sell it, but you're not obligated to buy it. That way if you've built up a good sized book, he can't change the price on you to keep the book and if it turns out to be a crappy book, you're not overpaying for it.
Just some thoughts...take them as you wish.
BTW, you'll usually get better responses around here if you make sure your posts don't come off rude. Just ignore the responses you don't like and thank the people who give you what you want. I took pity on you, but normally I would have seen your responses and said to myself, "that *ucker gets what he deserves.
Good luck and keep us updated on what happens.