Talent is so hard to find, recruit and keep that when one of your strong performers announces that they are departing to lead another law department, do you feel good for them or do you gnash your teeth? Deep down you realize that ambitious, capable lawyers won’t want to wait for you to retire or move on, but, still, the loss of a star hurts (See my post of June 24, 2007: mixed feelings when a strong performers resigns; and Dec. 19, 2007: inevitable departures of some talented lawyers.).
Be magnanimous. That should be your goal. Feel proud that you have groomed a lawyer so good that another company entrusts them to serve as their head of legal. Feel good that the lawyer is confident enough to grab the ring. Feel optimistic that you now have an opportunity to develop some other careers in your department.