In the ending of the poem, Piercy has constructed a vision of woman as a result of industrialization.  The idea of a fan belt being "worn out" has yielded a product that has broken due to overuse.  In a very odd way, the modern woman has become the version of Boxer from Orwell's Animal Farm.  Both work to please an external order that has little or no regard for their state of being or their own existence.  Instead, government and society view both Boxer and women as means to ends and when this end has been accomplished they are disposed of without hesitation.  The ironic manner in which the people view the Barbie doll vision of women in the funeral parlor reflects that the woman has served her purpose in society.  The feeling of the "happy ending" is rendered and used to mask the suffering of the woman.  It is a way for the patriarchal society to maintain control of the use and disposing of women.  In this case, of course, Piercy is saying that because of women’s subservient position in society, it is often difficult for their lives to have happy endings.