I'm nidan and regularly teach at our dojo. If I found myself living somewhere with no dojo, I might even open up my own... and of course my techniques aren't completely lacking in holes yet!
So if I was the teacher in that situation, what I'd like my student to do is: take the ukemi during the demo (because that way the others can get to work), and then tell me "sensei, I think there was a point where I could have stopped you/escaped/etc". Then I'd experiment with the uke to see what was going on. If it turned out that I had made a mistake, that would be a good learning point for me, and a valuable pointer to the rest of the class. And if I had been extra careful with the uke, I'd have a chance to tell them in private, without embarrassing them in front of the whole group.
Actually, since there are usually other yudansha attending the classes that I lead at our dojo, this really happens quite frequently.
Sometimes even with all of us there we can't find a solution right then and there. Then it becomes a question to take back to my teacher.