2. Develop a plan to capture and transfer the knowledge.
Now you know the key areas of knowledge which need to be retained when the leaver moves on. How do you must effectively capture it and transfer it?
The answer to this depends very much on whether it is a job handover, where someone will be filling the leaver's post. If this is the case, then the best plan is to set up a meeting or meetings between the leaver and his successor. You can then give the successor accountability for capturing all the knowledge they think they might need. In certain circumstances, where there are other customers for the knowledge in the successor, you might like include some of these people in the meeting.
If there is no clear successor, or (as in the case of a global expert leaving) the knowledge is needed by a whole community of people, then alternative approaches are needed.
Although the leaver could try to capture all the knowledge himself, it is better to do it with a facilitator, or an interviewer, or (best of all) a representative of the network or community.