Most organizations bend over backwards to retain key talent. Often this results in an employee staying at a company for the wrong reasons- golden handcuffs, guilt, fear, etc. I believe organizations should focus instead on encouraging employees to "graduate" when the time comes. This seems counter-intuitive. Why invest in an employee that is going to leave?
No doubt, organizations need a return on the investment they make in their employees. But there may be diminishing returns on that investment over time or the employee may not be 100% on board with their role or they may have outgrown their potential in the organization. Whatever the reason, I believe there are few instances of a healthy lifetime employee/employer relationship. People and the organizations they work for rarely evolve synchronously over a long period of time.
Perhaps the most desirable form of graduation is an employee becoming an entrepreneur. This can also serve the "parent" business by outsourcing work to the former employee's startup. Ricardo Semler's "Maverick" demonstrated the success of this approach. I have seen it here with our former employees that now run Joyful Noise Recordings and Ayokay. Not everyone is meant to run their own business but I do think organizations should build entrepreneurial employees (also called "intrapreneurs"). In many ways I feel this is the civic duty of business owners. An entrepreneurial minded employee can be a very powerful asset to an organization as well as their community.
I believe business owners should focus on their employee's overall growth, not just their growth within the organization. If you don't make this investment then your employees will be more likely to leave. Don't underestimate the real value of employee happiness. In my experience, growth equals happiness. But every organization has limitations for employee growth. So when an employee's growth slows it may be time to help them pursue a new opportunity.
Don't forgot, employees are brand ambassadors. When they leave your organization they will carry your brand with them. What do you want them to say? Don't you want them to tell a positive story about their experience? Don't underestimate the harm your brand can suffer when your employees suffer. I have seen this greatly undermine companies. No-one wants to work for or with them.