11. Sam Perkins
The Mavs joined the NBA as an expansion franchise in 1980, but some early genius trades set them up nicely. Dallas was part of the NBA creating the Stepien Rule, and it allowed them to select fourth overall after reaching the playoffs for the first time in 1984. The reward was Sam Perkins, a 6’9 forward that made an instant impact. The Mavs reached the playoffs in each of his first four years, including going to the conference finals in 1988.
Perkins was a starter and key contributor for six years before leaving to join the Lakers in free agency in 1990. He played with Michael Jordan and James Worthy at UNC and helped the Tar Heels win the NCAA Championship in 1982, and Perkins was a key member of Team USA winning the Olympic gold medal in 1984. Perhaps, he was always destined to leave.
Perkins was fantastic over the next seven years, including helping the Lakers, SuperSonics, and Pacers reach the NBA Finals. The former Mavericks big man has a fantastic story. Along with playing with many of the all-time greats, he has also done a ton of charity work.
Sam Perkins would likely rank a bit higher on this list, but the Dallas Mavericks likely did not have any chance to keep him in 1990. Still, they left the 6'9 forward depart just as he was entering his prime without getting a return.