Most people will be vaccinated or have the opportunity to be vaccinated by the time the 2021 season gets here. The season should happen with no issues. Fans should be let back in as well. I can still see some Demonrat run states like PA keeping fans to below 50% but that should not be the case. Masks may still be required but limiting the number of people should not. If you don't get a vaccine, you are at your own risk no matter where you go or what you do..
I bet stands won't be full again with no masks for another 5 or so years in PA. The states that are allowing fans over 10,000 now will probably have full capacity next year.
I could be wrong. I've been wrong about the virus many times. But I believe 70% vaccination equals herd immunity. The virus doesn't get a living host and therefore essentially disappears with the exception of the very unlucky. I believe this happened with H1N1.