I think they have crunched those numbers already because what is stopping them from doing that today? If there is more money in it, you better believe the NFL will do that in a heartbeat, regardless of local blackout rules. What if you could buy the games you want from iTunes? How much would you have to pay for a game to return the same profit? There might be a large drop in revenue if the move to a pay service was made and it didn't go well. Your advertising revenues could drop because not as many people would watch, or maybe more would go to a bar to watch, etc.
The national distribution of the games is key to all that advertising money, I just don't see how that changes because the local games are televised if they aren't sold out. Those folks will instead be in front of the tv, right where those advertisers want them. I think stadiums get smaller and the ticket price goes up along with an enhanced experience at the stadium, that's all.