That's what I was thinking. I saw in another post, on another board, that you'll be taking a shuttle to WDW, from your resort offsite. I think that last one gets there around 10pm-ish.
Here's the issue...offsite resorts/hotels really don't give you the best transportation options for WDW. It isn't going to be easy. So, you need to carefully plan how to get back to Epcot for that last shuttle. IF you're at Epcot and want to watch IllumiNations, watch from the side of the lake that is closest to FutureWorld...I think you might be able to watch from between the two shops that are right at the entrance to WS as you cross over the waterway from FW. Then, you can start heading back to the bus stops as soon as the show is over.
If you're at MK? You'll need to head out by 9ish...you have to get to the TTC and then onto the Epcot monorail. That could take up to 45 mins.
At DHS? Take the bus from the front of DHS to Epcot. You should plan on being at that bus stop no later than 9:30.
AK? The park usually isn't open that late at night, so that won't be an issue.
If you want to head to Boardwalk for the evening? You can take a bus to the resort, or walk over from either Epcot or DHS. Your best bet would be to head there after your AK day. Then, you can spend some time at Boardwalk and then head over to Epcot. If you have park hoppers, that will work. Otherwise, you'll have to head to DHS and take the bus from there to the front of Epcot. Or, just take a cab to your resort/hotel.
Depending on how far your hotel/resort is from each park, you may want to consider taking a cab.