You can give the official a clear idea of the pending projects.
You won't write this letter until you hit the retirement age of your choice, but it's a good idea to get prepared to do so, especially if that day is coming in the next few months. Make sure you provide enough notice of your departure. If you are moving, provide your boss with a new address.
Retiring is similar to leaving your job for any other reason.
For example, while it's perfectly okay to tell a manager how much you learned working for her, it's not a good idea to get emotional about it. Consulting is less time consuming and allows you to focus on the aspects of your work you enjoy the most, so consider offering your services in that capacity.
Learn how to create tax-efficient income, avoid mistakes, reduce risk and more.