Was listening to the Dan Patrick show this morning and he had Tony Dungy on talking about this very topic. Dungy stated that he did not believe this is the case. That all throughout history as the game changed people claimed the exact same thing but it still remains the most popular pro sport in the U.S. I tend to agree with Dungy and don't think any rule changes are going to kill the sport. It could take a pretty major shot if/when they lose the court case but it won't kill the sport itself.
Patrick also mentioned that moving towards a stronger PED testing system will also help. Each year you have guys getting bigger, faster, and stronger being able to cover sideline to sideline. Having an ever evolving PED program that includes HGH could have a profound impact on the sport causing a dramatic drop in the use of them. Only the marquee guys who make enough to pay the top doctors will be able to stay above the curve with newer designer PED's.
As for the guys who have come before the present group the care they have been shown is absolutely pathetic. If not for them the NFL would not be where it is now and they all need to step up immediately and start caring for them. Being that if they don't start now the current guys will take their places once they decide to retire.
French writer Alexis de Tocqueville warned about when visiting this fledgling democracy in the early 19th century – that this "American republic will endure until politicians realize they can bribe the people with their own money."