When coworkers leave, I don't question their business decision. I might think, "hope they handle the weather change in the northwest." But I don't think, "where is the loyalty? Can't they at least see this project through?"
The way I do look at this is maybe it galvanizes the team. It the flip side - maybe this is a symptom of a bigger problem and other players have been gripping and talking about leaving. That is the interesting angle to me. One player leaving is almost not interesting at all.