It is not unreasonable for there to be a viable solution and if someone is by themselves in the park and has a breakdown, it is not unreasonable to expect Disney to have the ability to assist with getting them out of the park and back to their vehicle, due to the unique design of theme parks anything short of that would be negligence.
The issue may have been that yours was a rental, Disney expects the rental companies to enter the parks to handle broken equipment.
You may think my point as to how it would be considered a medical emergency is inane, but it really isn't, it is the honest truth.
And consider how many cast members show up when someone faints in the park and how many of them spend several hours with the person. I had a friend once who fainted in Disneyland, there were at one point 20 CMs, including the president of the resort. I would say about 5 of them spent near 3 hours with us, so I really don't buy into the idea that Disney can't spare a cast member for an hour.
An no, they wouldn't need to navigate the monorail, ferry, etc., they would use their own transportation (i.e. vans, golf carts, etc.), which would dramatically reduce the transit time to the vehicle down to around 30 minutes or so. The person would get escorted back stage to the waiting vehicle and then transported to their car if time was indeed an issue. The point is the motorized cart would be used to transport to and from this vehicle as needed. There are many viable options to assist with this and yes, Disney should indeed do so.