When Should Team Members Know of Divestiture?

The company that I work for chose to create a separate business unit for a product line and noted it was not in an effort to divest the BU later but in fact, that is what they did two years afterwards. The team members who were part of that BU were quite upset as they felt they had been lied to. However, if the company had been honest, I don’t know if they would have remained with the company for so long. Thus, I am wondering when the appropriate time is to inform team members of an initiative that would ultimately impact them. Team members are not stupid, yet they also felt deceived.