I recall personally at Epcot World Showcase, grown DD and I had a late dinner that ended after hours, and we were slowly walking along the lake. We saw no other visitors around, but there were probably some scattered people here and there. Around Mexico pavilion, a CM asked us if we were taking the bus, and where we were staying. We said "yes" to the bus, and she said something into a hand-held radio. When we got to the depot there was a line of Disney buses, waiting to take us and others back to our resorts. Very well organized and efficient!
I read a post on one of the WDW visitor sites from a guy who took his friend to MK. His friend was a first-time visitor and a non-believer in "Disney Magic." They were extra late leaving the park and nobody else seemed to be around. Outside the gates they headed to the bus depot. No buses or taxis -- nothing. The new visitor thought they were stranded and started to panic. His "veteran" friend told him it would work out (although he didn't know how). Soon, in the distance they spotted headlights. And as the lights came closer they saw it was a Disney bus coming their way. The bus pulled up close to the guys and the driver asked where they were going. Then he said "come aboard" and drove them to their resort, on an otherwise empty bus. The newbie visitor suddenly understood "Disney Magic."
OP, no one gets left behind at WDW. Even if you drive and your car doesn't start, Disney will get involved in getting you and your car taken care of. It's really amazing.