I have only been at Epcot during Illuminations on the off season but I am pretty sure the World Showcase counter service places close when it starts. Anyone?
If you are going on an EMH night, then some of the QS locations stay open until late. Otherwise, I believe the PP is correct, most of the WS locations close with the start of Illuminations. If you were in line when the show starts, they will still serve you.