Once you re-think what you mean by a “job” in terms of what you’re hiring, you’ll see that there are lots of ways to engage a forgotten and ignored audience, your alumni.

If people changing jobs is the new normal (see also: gig economy, freelancer nation, professional nomads), you can change how you respond to them. As you wish them well with sincerity, as you offer to give them a glowing recommendation on LinkedIn. Leaving is the litmus test for employees: this is the moment when they are going to disappoint you, and you have no clear incentive to be nice any more. They expect you to give them shock and anger. Instead, give them excitement in their new journey and wistful regret that you couldn’t keep them longer. In return, they will repay you in multiple ways.