If Tom Brady retires, he will enter the Hall of Fame as the most accomplished quarterback in NFL history.
If Brady retires, the NFL will not miss him.
These are not contradictory statements.
Brady's résumé is not only unmatched in league history, he has created enough distance between himself and his competition, via championships and statistics, that it could take decades before anyone even challenges him.
But his retirement will not parallel Michael Jordan's, or Wayne Gretzky's. His retirement will not damage the league he dominated.
Basketball requires star power and personality, and Jordan became the most magnetic American athlete since Muhammad Ali, and unlike Ali he performed every two or three nights.
Gretzky made hockey entertaining even to those who didn't like hockey.
What Brady did was operate at a ridiculously efficient level while playing for good teams.