#2: Patty Mills
Nets guard Patty Mills spent a decade with the Spurs and emerged as one of the best backup point guards in the NBA before signing with Brooklyn in 2021. With one year remaining on his contract, the nearly 35-year-old will be on his last legs by next summer. Even then, the Spurs could always bring him back to serve as a mentor to a young team, much like how the Miami Heat utilized Udonis Haslem. Or perhaps they offer a second-round pick to acquire Mills via trade before or during next season.
A few things could prevent a reunion, however. The first is that the Spurs would likely have too many roster spots accounted for to offer one to a player who probably wouldn't play. Then again, Mills may want to actually play, which could take him elsewhere.
Of course, he could instead choose to retire, in which case he could join the Spurs coaching staff. Based on that, the possibility that Mills rejoins the Spurs in one way or another seems to be higher than that of most of the other former Spurs on this list. Here's hoping that happens.