The crux of this is a simple question: if the company is really interested in honest, constructive, confidential, consequence-free criticism, why only ask the ex-employees?
Companies that really do value honest, constructive, confidential, consequence-free criticism (the best kind in some cases) will value that feedback most from their current employees. But, in doing so, eliminate the need for the soon ex-employees to feel the need to dump reality on management.
Companies that really do value honest, constructive, confidential, consequence-free criticism (the best kind in some cases) will value that feedback most from their current employees. But, in doing so, eliminate the need for the soon ex-employees to feel the need to dump reality on management.