So, for regular MK Disney After Hours, it has typically only been bus available back to Poly (shares with GF most of the time, but has shared with all of the MK resorts at times in the past).
For Villains After Hours this past summer, they did run the resort monorail (maybe boats too, I’m not sure, although I’m pretty sure they did) all the way through until after the event.
I’d keep an eye on the thread for updates once we start having VAH events next year to see what they are up to this time.
Of course at Poly, you always have the option to take the Ferry to the TTC, which will definitely be running .