If we interpret Prince Prospero's desire to avoid the terrible disease, the Red Death, as a basic desire to elude death itself, then the masked ball essentially ends with the lessons that one cannot escape or elude death and that it is mistaken pride that leads us to believe that we can. Though his kingdom is in dire trouble, the prince decides to handpick his most healthy and fun courtiers to party with him in a far-away abbey that he owns and outfits to be impregnable. He seems to believe that he is more powerful than death, that iron bolts and chains and gates can keep death away, that his wealth and status provide him the opportunity to do something no human being can do: hide from death.
In the end, then, the prince runs through the series of seven rooms he has designed (rooms which seem to represent the span of a human life, ending with death in the red/black room with the ebony clock -- another symbol for mortality) toward the masked figure that represents the Red Death, and he dies instantly because "Darkness and Decay and the Red Death held illimitable dominion over all." Death is a necessary and inescapable part of life, and no one is immune; therefore, it does hold dominion over all. Despite everything the prince has done to shield himself from death, the ending of the ball (and the story) shows that it simply isn't something we can control, no matter how rich or prosperous we are.
When Prince Prospero encounters the horrible, blood-stained figure among his guests, he is enraged and determined to unmask the stranger. None of the bystanders, however, acted to seize the figure who moved with "solemn and measured step" through the various rooms of the Prince's abbey. The Prince chases after him, brandishing a dagger. When the figure arrives in the last room, he turns suddenly to confront the Prince. The Prince cries out, the dagger falls to the floor, and then the Prince himself falls dead. The guests rush in, attack the masked figure, and find to their horror that there is no person under the costume. The guests then fall dead, one by one, "each in the despairing posture of his fall."