Zach Collins was the first rock to get rolling. With him followed Nigel Williams-Goss, and to a certain degree, Johnathan Williams. After that, two more scholarships left the Gonzaga Bulldogs, with Bryan Alberts declaring his intent to transfer and Ryan Edwards leaving the game. None of this even takes into account Jordan Mathews and Przemek Karnowski graduating.
All this goes to say, the Gonzaga Bulldogs, talented as they may be, have some serious production to make up with all the players they are (might be) losing.