Did you ever have to contact your former supervisor after retirement for any reason?

Employer yes--you should sign up on the Benefeds website, and make sure you are registered on the Office Of Personnel Management website and have your paperwork in order. All your questions and correspondence will go through those two main sites, and if you had a TSP account, you'll also need to make sure you are up to date on that website as well. 

I never HAD to contact my supervisor again, but I did stop in to say hello a couple times. We got along well and it was nice to see them again. 

Never had to but we were friends outside of work and still are after my retirement (mine was private employment  not government)

In fact he has called 3 different times asking if I was ready to come back to work

I am still invited to the office parties at Christmas, etc.   It's a good idea to keep a good relationship, just in case you would need help.   

Not likely. Why?

No, my former employer kept contacting me because I punched out and quit mid-shift, and then I retired on my savings 10 years ago. Every great once in a while I Google Earth to look at the Pie Factory.