That sounds frustrating. I will have a car but I will be alone so there is no way I can get the scooter into the car. I need the car to go visit my daughter at some point.
It happens to most of us at one point or another; you roll up to the bus stop and there are 2 mobility devices ahead of you.
OR you roll up, think "Yay! I'm the only one!" only for the bus to arrive with both spots already full, and those folks are riding on to the next stop.
This is why if you have a hard-and-fast, can't miss it ADR, or other time-dependent experience waiting for you, allow *at least* 90 minutes if using the internal Disney transportation. Any kind. Boat, bus, Skyliner, Monorail - it's all subject to the same whimsy of man and nature.
If I'm traveling from Poly to Hoop Dee Doo over at the Fort? 2 hours. I allow 2 hours. No joke.
If I want to be at my 10:30 ADR at Epcot, and I am at AKL? 2 hours. No joke.
If you realized - whether because there are multiple people at the bus stop, or you see them when the back doors open to let the temporarily-able-bodied walk off the bus - that you are going to miss this bus? Try to approach the Driver. Remember that it is not their fault that you will not get on this bus; (after all, they are just doing their job), and ask them nicely if they know how far behind them the next bus is.
You can't always talk to the driver; that's OK - every bus stop at Disney now has the electronic bus boards, showing the anticipated arrival time of the next bus to your destination.
If you don't want to/can't wait, then you have option to use an accessible Minnie Van. The cost varies (based on time of day, time of year, how far you are traveling around Disney World, and if the wind is from the right direction) but you and your
ECV will arrive in style. You don't have to sit on the ECV if you use a Minnie Van; you can siti in any seat besides the Drivers.