Kevin Grier and I have a new piece up on Grantland, on that topic. It is perhaps hard to excerpt, but here is the close of the piece:
Another winner would be track and field. Future Rob Gronkowskis in the decathalon? Future Jerome Simpsons in the high jump? World records would fall at a rapid pace.
This outcome may sound ridiculous, but the collapse of football is more likely than you might think. If recent history has shown anything, it is that observers cannot easily imagine the big changes in advance. Very few people were predicting the collapse of the Soviet Union, the reunification of Germany, or the rise of China as an economic power. Once you start thinking through how the status quo might unravel, a sports universe without the NFL at its center no longer seems absurd.
So … Tennis, anyone?