In Death of a Salesman, what harm and what good does Willy's death do?
I have changed your question as it asked more than one question. The part of the play that you would benefit from analysing is the Requiem, the last section when the characters are together after Willy's funeral. It appears the impact of Willy's death on his family is overall negative. Linda in particular has problems understanding Willy's motives for killing himself, and dwells on the good times. There is a harsh irony in the fact that they have just finishing paying off their mortgage. Happy intends to dedicate his life to his father by continuing to live his dream and set up a company called the Loman Brothers. It is clear that Biff things Happy has learnt nothing and is misguided, as his look of despair that he gives to his brother illustrates. Significantly, he says that his father had "the wrong dreams". It is Charley alone who is sympathetic to Willy and also explains that a salesman has to have a dream.
Certainly, Biff, with his statement, "I know who I am kid", seems to have gained some self-knowledge through his father's life and death, realising the danger of having the "wrong dreams". Happy seems to still be sold on the same dreams that led to his father's death, whilst Linda is just bewildered about the death of her husband. Linda's statement, "We're free", which is repeated three times, has many possible meanings. Willy is now free from earthly unhappiness. The couple are free from the need to earn money to pay for the mortgage and, in another sense, the good side of Willy's death is that now the family is free to act without the crippling pressure of Willy's dreams.