Blackballing, like blacklisting and other exclusionary practices, essentially means "you'll never work in this town again."
The National Wrestling Alliance had a red card system to keep the many territories under its umbrella informed if a particular wrestler was blackballed by one of its promotions. Even WWE, where they love to tout that anything can happen (if it's right for business or, laughably, if the fans want it), there are still several names who are personae non grata in Stamford and all points north.
But, like retirement stipulations and "loser leaves town" matches, blackballing is rarely permanent. Ultimate Warrior, Madusa, Kurt Angle, and others were blackballed or on WWE's sh*tlist for years, only for time (or money) to heal all wounds and allow them to be welcomed them back into the fold.
As several wrestling personalities have said, Jim Cornette included: "That guy is blackballed forever... until the next time someone books him."
Hell, it's been a long time since we've seen Hulk Hogan, but he'll be back.
That being said, sometimes it sticks, and someone stays gone for good. Other times, they build a reputation for getting blackballed as much as they get booked.