I'm reminded of "The Indispensable Man" by Saxon White Kessinger:
Sometime when you're feeling important;
Sometime when your ego 's in bloom;
Sometime when you take it for granted,
You're the best qualified in the room:
Sometime when you feel that your going,
Would leave an unfillable hole,
Just follow these simple instructions,
And see how they humble your soul.
Take a bucket and fill it with water,
Put your hand in it up to the wrist,
Pull it out and the hole that's remaining,
Is a measure of how much you'll be missed.
You can splash all you wish when you enter,
You may stir up the water galore,
But stop, and you'll find that in no time,
It looks quite the same as before.
The moral of this quaint example,
Is to do just the best that you can,
Be proud of yourself but remember,
There's no indispensable man.
Update (1/27/2017): It was not a voluntary termination. Sure, per tradition and as the same with other senior officials, they had tendered their resignation to the new President, who then was free to accept or reject their resignations. The President accepted these particular four individuals resignations by informing them that their services would no longer be needed. (Warning: video plays automatically).