Leaving Selden's apartment, Lily goes to rest in Bryant Park. She knows that there is nothing for her at home except a bed and her bottle of sleeping medicine. As night comes on, a passerby asks if she is sick before recognizing her. The passerby is Nettie Struther, a character we have not yet met but who met Lily when Lily saved her from an illness while participating in Gerty's charity organization. Although Nettie was sick, she has totally recovered, and is enjoying a successful marriage with her husband and their newborn child. Nettie, seeing that Lily is sick, takes her home to her house, where Lily warms up in the kitchen while Nettie tells Lily of her success in working her way up from the gutter to a happy family life. After briefly holding Nettie's baby, Lily says she must leave, but promises to return another day. The encounter has made her happier and stronger, although only briefly.
At home, Lily begins to furiously sort out her various possessions for no apparent reason; she is interrupted by when a servant delivers a letter to her containing her check from Mrs. Peniston's estate. Shocked, Lily begins writing checks to pay off all her debts to Gus Trenor and other outstanding loans. She realizes that even though she is now free of all debt, she has absolutely no money, and all she can look forward to in life is a prevailing dinginess enshrouding middle age. Extraordinarily tired from lack of sleep, Lily takes out her sleeping medicine to help her doze off. In the medicine, she sees a long escape from the dreariness of her life, and decides to take much more than the prescribed amount in hopes of sleeping for a long time. In doing so, she overdoses on the medication and dies in her sleep. Whether or not she knew she was committing suicide is left ambiguous and unresolved by the novel.
The next day is marked by beautiful weather, as Selden sets out from the Benedick to visit Lily. Realizing his love for her and her desperation, he has decided to propose marriage to her. When he arrives at her apartment, however, he is greeted by a distraught Gerty Farish, who has found Lily's dead body. Gerty leaves him to take care of Lily's papers and belongings, but before Selden can leave, he feels tempted to lie down next to Lily and rest his head on her shoulder, which he could never do while she still lived. Getting up, he goes through her check book, and finds that she received the estate check and paid off all her debts, including the one to Trenor. He cannot decide, though, if the check to Trenor explains the mystery of her demise or only deepens it. The novel ends with Selden and Lily, alone together at last, as he realizes how much he loved her and how his own cowardice had kept them apart at the crucial moment when they could have been married.
One may ask why Wharton chooses to introduce a new character, Nettie, so late in the novel. For one thing, Nettie contributes to the ironic structure of the novel's narrative. Obviously, Lily has gone from a position in which she could offer help to one in which she needs help from one who she had earlier saved. Perhaps more importantly, though, Nettie provides a symbolic foil, or counterpart, to Lily. Nettie represents the things that Lily could have been (and perhaps even still could be). We learn that like Lily, Nettie suffered from dire mental problems, but after healing herself and returning to society, she had success in finding a husband and starting a family. Because Lily could feasibly meet with the same success as Nettie, we have to frown upon Lily's death as a waste. Even though Lily feels hopeless, Nettie proves that no situation is so entirely hopeless as to warrant death.
The actual ending of The House of Mirth is one of the most ambiguous endings in all of literature. Perhaps the most fundamental question is whether or not Lily commits suicide. On the one hand, she desperately wants to sleep for a long time. She sees no way out of her current situation and can only imagine for herself a long life of the dinginess she has always hated. On the other hand, Lily has made promises to get together again with Nettie, and she has asked Rosedale to visit her often. She also tells Selden that she will see him again, but not for a long time, as though she were going to take a long vacation by herself. Furthermore, with the reception of the estate check, Lily is no longer in debt; she is free of any slavery impulses.
Given that there is no right or wrong answer that explains Lily's death, we must interpret its meaning. Overall, Lily's death completes the downward spiral which the whole novel has chronicled. Death is, as we saw earlier in the book, the final state of rest for anyone; it is the absolute lowest rung on the social ladder, which Lily has been descending throughout Book Two. Structurally, then, one can argue that Lily's death makes sense and is necessary. However, thematically, Wharton seems to condemn Lily's death by introducing Nettie. If a character like Nettie can rise up out of total despair, we have to assume that Lily could as well. Furthermore, Lily's death seems so unnecessary in light of the fact that so many people are willing to help her in every way possible. No one should die like Lily does if he or she has a good group of caring friends.
Perhaps the final question is whether or not Lily's death ties up all the loopholes or only opens new ones. The question will ever remain of what would have happened to Lily if she survived. One thing to keep in mind is the remarkable role of luck in the novel. Throughout Book Two, Lily has been through one long, particularly unlucky spell; sooner or later, the odds of that would have to change. Also, because Lily dies only hours before Selden arrives to propose marriage, what would have happened to her if she had survived and married Selden? Selden is particularly confused by her check to Trenor. One of the most peculiar aspects of the novel is why Lily felt so unerringly bound to repay Trenor when she could just as easily have forgotten all about her debt without consequence. Had Lily taken the estate check and begun a new life altogether, she would have been off to a great start. This is one fact that confuses Selden at the end of the novel.
It is important to keep in mind that there are no definitively right or wrong answers to any of the ambiguities raised in the last chapters of the novel. Wharton's intention is clearly to leave a number of loose ends for the reader to interpret; this is what makes reading fun, and this is one of the reasons why The House of Mirth is considered an American classic.