The money is too good for these guys to say no....some will and some won't. With the medical info that is out there and the awareness, these players have a choice to make. I don't see the NFL ever falling.....it is too good of a sport. I suspect sometime in the future that players will have to sign a waiver as part of their contracts. For all the ones that don't want to play to save themselves from years medical issues, there are hundreds to thousands more lining up to take their place.
You have a valid point about potentially losing the premier athlete to another sport.