I would like to add a little bit of Hemingway's personal background to help understand the unsettled, and unsettling, conclusion, of "Hills."
Hemingway had to deal with the problem of abortion when he was married to Hadley Richardson. David Wych explains in his 2002 article from "The Hemingway Review":
Before Hadley's second pregnancy proved a false alarm, Sally Bird urged him to "[s]top acting like a damn fool and crybaby" and offered him the obvious ultimatum: "Either you do something about not having it, or you have it" (McAlmon 277). Reynolds, noting that "[t]hey all knew abortions were available in Paris," nonetheless asserts that "a boy raised in Oak Park did not easily accept that solution" (The Paris Years 219). Just how Hemingway did think of abortion is reflected in letters he wrote to Pauline Pfeiffer in the fall of 1926, some eighteen months prior to the completion of "Hills" when the lovers were expecting to remain apart for one hundred days. The separation was imposed by Hadley, according to an agreement under which she would grant Hemingway a divorce at the end of the prescribed period. To his future wife he wrote, "when two people love each other terribly much and need each other in every way and then go away from each other it works almost as bad as an abortion" (Lynn 363). With this statement, Hemingway set a precedent for using the termination of a pregnancy as a metaphor for the pain of separation between lovers.
There is very little conclusion to this story. The man and woman, who have been arguing over whether or not she should have an abortion, cease their argument. The woman pleads for the man to stop talking to her about it, threatening to make a public scene if he doesn't. He moves their bags and gets himself a drink. When he returns, and asks if she is ok, she responds that she is fine. Obviously she isn't. But by this word, she has ended the argument. No decision has been made.
However, many readers feel that by giving up the argument, the woman is agreeing to be led by the man, and that - were the story to continue - she would have an abortion.