When I worked at the Refreshment Port (near Canada) several years back, closing time was as soon as we had cleared the line of people after Illuminations started (usually 9:00). Often there was a healthy line of people buying Hot Chocolate, snacks, etc. before teh show, but once Illuminations started nobody else joined it. We were not allowed to roll down the shutters until there was nobody else waiting.
Bascially it was a race to clear the line before Illuminations ended while everone's backs were turned watching the show. It was such a hurry since once Illuminations ended, we would get a huge line again from all the people stopping on their way out. If you didn't clear all the guests during Illuminations you were likely to spend at least an extra 30 minutes or more serving everyone on their way out.
So closing time for the food locations is at park closing, but as long as you are in line at that time, you should not be shut out.