What kind of closure does the Requiem provide to the play in "Death of the Salesman"?

The setting of the brief Requiem at the play's conclusion is the cemetery following Willy's funeral. Through this scene, we experience dramatic closure in that we see the various characters' emotional reactions to Willy's death. In their concluding words and actions, several of the play's themes are finalized, with sad irony. 

Happy shows no moral growth or increased self-awareness as a result of his father's death. He continues to make the same unrealistic, empty promises that have characterized his adult life. We leave Happy with no hope that he will ever grow up or behave responsibly or unselfishly.

Linda remains the same loyal, loving wife she has always been, still lost in denial--or not. Linda truly may be unable to grasp the reasons behind Willy's self-destruction, or she may be continuing to live as she has always lived, denying truths she cannot face. Linda's words are steeped in irony: "I can't understand it," she says. Her final words are equally sad and ironic: "We're free . . . We're free . . ." 

A final thematic irony in the play is made complete in the Requiem. Biff continues to insist that Willy did not know who he was, implying, of course, that Biff knew who Willy was. It seems clear, however, that only Charley knew who Willy had been:

You don't understand: Willy was a salesman. And for a salesman, there is no rock bottom to the life . . . . He's a man way out there in the blue, riding on a smile and a shoeshine. And when they start not smiling back--that's an earthquake . . . . A salesman is [sic] got to dream, boy. It comes with the territory.

Biff may have come to understand himself and his own life in some negative and self-defeating way, but he never achieved a real understanding of his father, even though he believed that he had. Thus, at the play's conclusion, no one in Willy's family truly can appreciate his life--or his death.