When passionate employees become quiet, according to Tim McClure, it usually sends a signal that the work environment has become very dysfunctional. As a result, suspicion and insecurity clouds the culture, and employees retreat into self-protection behavior patterns to protect themselves from the forces within the company as opposed to the forces externally.
The leader must be aware and act on this immediately. When you have a passionate team inspired to help the company achieve its vision while fulfilling its purpose, you must do everything in your power to ensure that this team keeps this vibe. Otherwise, you run the risk of pushing away great talent while settling for mediocrity.