NFL Sunday Ticket won't get shut down. What will likely happen is the NFL pricing exclusivity too high for DirecTV to keep it. Then the NFL will give them a non-exclusive license, use that same model to shop it out to all their competition (Dish, various cable companies) and then the NFL will likely set up their own online/media box streaming system like MLB.TV, cutting out the middle man on the future of distribution.
This makes the most money for the NFL and DirecTV has already all but killed Dish. Sunday Ticket isn't going to help them beat cable particularly effectively, a lot of other ramifications go into those local market battles. It isn't worth the premium pricing.