All of the stores are open right after Illuminations. For how long I dont know. However, we normally hit MouseGears on our way out.
As the other person said, it's also nice to grab a bench and sit down for a little while and just enjoy the atmosphere. If you want some very good pictures.
After Illuminations, go to the back of WS (the back gets empty first) and just hang around a while (we did this and LOVED IT) and it literally will get nearly empty. You can take pictures of nearly everything with NOBODY in them.
If you have a cam with nice manual settings, you can get INCREDIBLE pics of Spaceship earth. It's empty enough to use a tripod. Just a tip.