I think you're referring to Hank Gathers, for Loyola-Marymount College. I don't recall what they did in his case, but I remember his best friend on the team (whose name escapes me) shot his first free throw of every game with his non-dominant shooting hand for the rest of the season. And if I recall, he made every single one of them. They made a movie about it, called, appropriately, "The Hank Gathers Story".
Reggie Lewis, for the Boston Celtics, died of a heart condition as well, but I believe that was during a practice session.
As I've been thinking about it this afternoon, I think they took him off the court. I don't believe they announced until later that it was "sudden death".
Then there was Len Bias, drafted by the Celtics, who died of a drug OD.