If they cancel the fall sports there will be no 2020-2021college sports. Nothing of substance will change between now and late winter/spring. A vaccine is not going to be widely available and if it is it means safety vetting was shortened which is troubling to many experts; and, we won’t know the length of immunity, or what may happen to some individuals on re-exposure in terms of ADE complications.
The first mistake: there will still be risk of infection in the spring. The FDA is ready, for example to approve a vaccine that is at least 50% effective. Assuming one or more candidates meet that bar, a vaccine that is only 50% effective accepted by 50% of the population and potentially requires two rounds of injection one month apart becomes a mathematical and logistical problem for meeting the media and college presidents demands of zero risk.
The second mistake: assuming the players are safer at home. Access to frequent screening tests, world class medical care, a broad support network, and non-idle hands. Oh, and they aren’t giving up on what is (for some of them)their life’s work and dream (to this point).