If the most important thing here is to avoid getting the virus until you are vaccinated, do you think there is even a chance at a 2021 season?
Maybe is my answer your question. But can't imagine a full normal season.
Lets say they have a vaccine by the end of the year. My thought would be the first people to get them would be the high risk (unknown amount of people, medical field (16 million), police (~800,000) , teachers and other school staff (3.2 million teachers) then the kids.
And you have to figure the rest of the world would do something similiar, so the low risk people wouldn't be getting that until much later in the year, thus pushing sports out again.
(and if they gave the professional athletes the vaccine prior to the teachers, thus not allowing kids to go back to school, well IMO could cause professional sports to lose money, because I would never attend a game again.)
But if you change 'most important thing here is to avoid getting the virus until you are vaccinated" to most important thing is minimizing the spread to allow life to go on, then baseball will happen for sure next year because there are enough people willing to go a little further than others and IMO there will be enough of those people to support a season.