Do you really think NFL will die, though? A large part of the reason that so many players get injured is because of the way they tackle. If they just learnt (and were forced to use) proper tackling techniques, there would be way less head and overall injuries.
I don't think we know exactly what causes the injuries. It could just be repeated (relatively soft) blows. Offensive and defensive lineman have some of the highest brain injury rate and neither are involved in many tackles, especially high-velocity ones. Also, with a limited budget, you have to take some risks if you want to make baseball #1.