Participation is a growing danger but IMO the real threat to HS football is liability. When school districts can either 1) No longer afford liability insurance 2) Get taken to cleaners in court for brain injuries ...that will stop HS football. The dominos fall from there.
As for blacks playing baseball - that door might swing back open as baseball continues its move into becoming "browner" as latin players come to the sport in bigger numbers and starring roles. This makes the sport more diverse. As people like Jeter and others take up front office and coaching positions the games diversity will act as a attraction. The money is there as is longevity. Sooner or later black mothers will start to decide to put gloves and bats in kids hands. If the peer pressure allows it - someday some young African American from Alabama will dream of playing center for the Braves rather than RB for the Tide. And there will be another Henry Aaron.