I wish they would keep transportation running later for resort hoppers / dining. Maybe they will do so with such short hours? I know that some restaurants even within the parks are reportedly accepting reservations after official park closing, so it’s possible they’ll keep transport open later.
Also keep your eye out for the walking path between MK and GF. It is reportedly finished - I bet it opens whenever the NBA is gone from GF. If you got stranded at Poly, you could always walk to CR (about 1.5mi, so quite the hike). Or you could start at Poly, then go to GF, then if monorail is closed, you’d be close enough to walk to CR without too much exertion.