Keep in touch. You may have people who'll want to keep track of you, and you may have friends you were in contact with using your work e-mail. Once you're gone, will people know how to get in touch with you?
I did an informal survey in the month after I announced my retirement, and found a common theme. A lot of people said that they never knew where their retired friends and colleagues were. Once you no longer have a fixed schedule, no one knows where (or more importantly, when) they can find you. If you want people to reach you, be sure to share your new e-mail address.