Do you return keyboard

No. In addition to the directions that you references, see the following from Apple Trade In - Apple

Do I have to include accessories like chargers and cables?

No, you do not need to include accessories. If you choose to include any, we will recycle them for you.

To be specific, you do not return either your keyboard or mouse. You do return the power cord. If you do not, your trade in price will be reduced $20 if i remember correctly.