Let's imagine that everything goes as well as could possibly go with his rehab. Assuming that he begins rehab starts and needs 4-5 starts to get his pitch count up to around 80 pitches and he makes his major league debut in August, he likely wouldn't throw more than 50 innings (and probably less assuming he's on a pitch count/innings restriction) in 2020. Even if his velocity returns and he pitches well in the limited time in the majors, I still can't imagine other teams are going to give up much for a pitcher who hasn't shown the ability to lead a rotation, is still coming off of yet another arm injury and is starting to approach free agency (I think that is 2021?).
That's why I think, for good or bad, the White Sox are better off just getting whatever they can from him, but in a lesser role when he returns. I don't think there is any scenario where they can depend on him to start the season in 2021 as a #1 or #2 starter. If he's a #3 starter, the White Sox are probably in major trouble still. He's likely a #4 type of starter on a contending team, but that will come with major risk.