I acknowledge that the ratings would, in fact, go down should there be no Tiger involved. But, do you really think the members care? When you have the likes of Bill Gates, Warren Buffett, Jack Welch, T. Boone Pickens, etc. as members, you really aren't too dependent on CBS contracts or have any money issues whatsoever. They aren't members because of CBS ratings. They are members because they want to be a part of an ultra-exclusive club that happens to have the most pristine golf course in the world.
The Masters/Augusta National will always have its tradition and the members can always give a big middle finger to anyone they please. They only have to answer to themselves and their collective egos are likely large enough to consider telling the best golfer on this planet to 17-off. If the ratings went down as a result, then they will just have an easier time planning for the crowds the next year.