Are you trying to think up the most complicated scenario you can?

Ok, I'll play. Admittedly on a party night if you were trying to go from the MK to a 9:00 pm ADR at Citrico's and boarding at the MK on the monorail loop was limited to monorail resort guests then yes, you would have a problem. However, why would you want to leave a hard ticketed event for a 9:00 pm ADR?
At those times of year when MK closes @ 8:00 it wouldn't be an issue because you wouldn't be hanging out at the MK until your ADR time (because the park would be closed). On an EMH night the monorail shutdown policies wouldn't come into effect until 9:00. Your hypothetical ADR is at 9:00, so you should have already departed the MK by that time.