You would
NOT have been without transportation on
MDE. Practically speaking, it is not a requirement that you make a reservation on MDE before you arrive. If you have a Disney Resort Reservation, you are entitled to a trip from MCO to your resort and a trip from your resort to MCO. What would have happened in your case, had you not asked about it, is when you arrived at DME, they'd scan your magic band and the system would tell the CM that you didn't have an MDE reservation. In the past, that would've meant they'd ask you to step to the counter while they set up that MDE reservation right there. They'd then send you on your way to the appropriate DME bus. I'm not sure they send you to the counter anymore. Scanning the MB will reveal the resort reservation details and could now result in an automatic reservation being created and the CM just pointing you to the right line. In any case, you would NOT have been stranded without transportation.
Steve