The latest to depart is Thomas Conheeney, who had served as president of Mr. Cohen’s former hedge fund, SAC Capital Advisors, and more recently in the same capacity at the billionaire investor’s family office, Point72 Asset Management, people briefed on the matter said. In recent years, Mr. Conheeney, who joined SAC about 15 years ago, served as the point man for Mr. Cohen in dealing with the firm’s work force, which once numbered 1,000. The timing of Mr. Conheeney’s departure, just four months after a federal judge accepted SAC’s guilty plea to insider trading charges, may come as a surprise to some within the firm. In announcing the name for Mr. Cohen’s family office in March, Mr. Conheeney gave no indication he was planning to move on.