Football may look different in 20 years but it will exist. We are already seeing a dramatic change in how it is coached and in the rules to reduce head injuries, there will be more changes to come.
If you are going to talk about head injuries in football then you have to recognize that while football is more dangerous it is far from the only sport in which the risk of head injuries exist. Lots of people say "I won't let my kid play football because I don't want them getting hurt. He can be a soccer player."
So something like this didn't happen
https://sports.yahoo.com/world-cup-...-causes-traumatic-brain-injury-190108282.html
The realities are that if we are going to have sport we are going to have some risk. The question is not eliminating risk but managing it. I knew a guy many years back who was rock climbing and ended up pulling a large rock down on his head. Fortunately he was wearing a helmet which he normally didn't do while climbing and only got hurt instead of killed.
We will see changes to football and there will be fewer head injuries but the risk will always be there and people will see play and watch the game.