LaMarcus Aldridge
He had a stellar career with the Trail Blazers, but LaMarcus Aldridge left Portland just when things were getting good.
The Blazers finished the 2014-15 season 51-31 and entered the playoffs as the No. 4 seed in the Western Conference despite injuries to Aldridge and Wesley Matthews. Aldridge was named Second-Team All-NBA that year and was seventh in MVP voting after averaging 23.4 points and 10.7 rebounds.
Playing alongside him was a 24-year-old Lillard, who averaged 21 points and made his second consecutive all-star team. That 1-2 punch would have helped the Trail Blazers contend in the West for another handful of seasons.
CJ McCollum broke out in that year's postseason playing in place of Matthews. Portland also had Nic Batum in his prime. The future looked bright - so much so that Lillard said recently that was the one team he believed could realistically win a title during his Blazers tenure.
Then Aldridge left to sign a max contract with the San Antonio Spurs where his stats began to drop. He was still an all-NBA-caliber player, but he never dominated the way he did in Portland. It's one of the greater what-if scenarios in franchise history.