As much as Al Horford preferred not to, leaving Boston was one matter; where he would take his talents was another.
Al Horford probably envisioned spending the rest of his career with the Boston Celtics. That changed when Jayson Tatum suffered a torn Achilles. Perhaps he would have departed in free agency anyway. The franchise had to reset and gain flexibility after consecutive campaigns over the second apron. Changes were coming, independently of Tatum's injury.
Still, as the Celtics' president of basketball operations, Brad Stevens, conveyed at media day, Boston tried its best to keep him.