I know you can't do much about it from the side coming in to replace someone, but waiting until someone is on the way out is fundamentally a flawed way to do it

I know you can't do much about it from the side coming in to replace someone, but waiting until someone is on the way out is fundamentally a flawed way to do it. As an employer you need to be focused on seamless onboarding _before_ the people who know how to do things have decided to leave. "Knowledge transfer" is just new-hire onboarding done by someone who no longer has a stake in seeing it succeed.