First off, try to request a window seating for a spectacular view of Illuminations. Even wait a bit if a window seating area is not immediately available when you arrive, The front desk should be able to advise you on availability, keeping in mind those seats are coveted at your dinner time. If you do leave the restaurant to view, I would say to just go to the promenade area between Mexico and Norway, excellent viewing.
As for leaving, just head on out through International Gateway, a nice after-closing stroll of World Showcase. It is very pretty after closing, great photo ops.
Enjoy.