If Quinn did not show up, Homer would tell the two presidents on stage to invite the guest to appear. Homer would use the excuse of saying that the guest might not have heard his speech and urge the two presidents to search for Quinn in the lounge.
Afterward, the two presidents would only find a bunch of corpses lying around the lounge with Quinn nowhere to be found in the lounge.
As a result, the scene would become a mess. As the host, Homer would have to stay calm in the face of danger. Home