If TV viewership gets bad enough that it affects team profits, and then the player's union contract, which is hugely based on TV revenue, I think that would knock some sense into players and owners and maybe even the blockheaded commissioner.
The teams already have their money from the TV contract, the NFL being one of the first pro leagues to institute revenue sharing. Whether or not these annual payments are tied to specified viewer levels I don’t know.
The networks, however, will have to lower ad rates if viewership falls. I can see them pressuring league management to do something when their revenues get hit. Are they going to let some second string QB in San Fran do that to them, just because he read a book (probably his first one) in the offseason? I don’t see Tom Brady, Eli Manning, or Aaron Rodgers doing this, only second tier no-names.