The man's got a problem. He is in charge of a movie show, and before the show there will be a lecture. But the professor who's going to give the lecture can't make it because of family emergency. He's got two solutions. One is to cancel the lecture and the show. The other is to give the lecture himself. If I were in his shoes, I'd opt for the first solution. He can send emails to the students, explaining to them what has happened. I believe the students can understand his situation. On the contrary, if he gives the lecture himself, he may not be able to answer all the questions raised by the students since he doesn't know much about the lecture himself and he's not confident. That would be quite embarrassing. Plus, chances are the students may get pretty disappointed.