We just got back. They run one more bus to every open park at closing time. 00, 10, and 20. HS to MK is at 9:20 but I can't imagine you would get back there unless you were at the corner of the show and full on sprinted. They load the busses 5min ahead of time. The Star Wars show is 12 minutes long. You can ask if they wait an extra 5min for firework goers to get back there.
I can tell you they did not at Epcot. We had a FP forTest Track and for some reason they were only half loading each room to design cars. We were in there for 40 minutes. We raced back to get the last 9:10 bus and at 9:11 it was already gone.

No biggie, we will take the monorail. Nope. It was closed.
Took one look at the bus line heading over to MK and took an Uber to the TTC.
So while I loved the Express bus service I really wished they would run 2 busses after closing at Epcot and HS to MK instead of one. Or make the last one 30min past the hour.
If you watch the ROL first show at AK, you can get back for the last MK bus, even with crowds. The show ends at 9pm and last bus is 9:30 when the park closes.
Same with Fantasmic. It gets over before 9pm. But right now there is no way to watch Illuminations or Star Wars and then get to MK on an express bus.