What do you do when you have a superstar who is going to leave? If at all possible, make it a long goodbye to facilitate a good succession plan, comprehensive knowledge transfer, and a smooth transition.
Ideally, you’d like enough time so the superstar can help train and develop her replacement. If you have that luxury, you should meet with the superstar and her replacement together on a regular, ongoing basis in addition to meeting with each of them separately.
Every step of the way, make certain that the knowledge transfer is being documented in detail in a set of tangible information assets that can be used thereafter as learning/training tools. Ideally, these tangible knowledge transfer assets would be in the form of indexed, searchable, and annotated step-by-step instructions (along with answers to frequently asked questions) for every task, responsibility, and project.
Remember, among the other best reasons to make certain that your departing superstars leave on the best possible terms is that they are likely to be valuable players wherever they go next and throughout the rest of their careers. Who knows? They might become your valued customers in their next career. Or valued vendors. Or maybe they will return and be valued employees once again, having gained the training and development resources of another employer in the meantime.