People began putting site navs in the footer so that the user wouldn't have to scroll all the way up once they were done reading the page. There were also accessibility problems with drop-down menus back in the day, so I remember being told that putting the expanded site menu in the footer would help that as well.
If you have properly accessible drop-downs on a sticky nav, I don't see the reason for putting a nav in the footer. I've noticed a few sites removing the footer nav when the sticky nav is added (look at mailchimp's new site).
The exception would be if the nav menu isn't sticky on mobile devices (which most people say it shouldn't be due to screen real estate). Then those users might still use a footer nav menu.
The BEST idea would be to track the links in the footer nav to see if people use it. If they don't, get rid of it!