In life as well as in presentations, surprises happen. You never know for sure what will happen no matter how carefully you plan. Events that seem like a fiasco as they occur and will later become a source of amusement. Birds were flying inside the conference room. Boisterous Marines celebrated a reunion in an adjacent room.
Bad things happen to the best presenters and program planners no matter what precautions they take.
How you react is what people will remember. Smile even though you feel like strangling someone. Keep your cool and sense of humor. Make the best of the situation. The speaker does not show or is late.