As we are trucking along through the story, we come to appreciate the all-knowing, all-seeing narrator who gives us all sorts of insight and information to add layers of emotional complexity to the events. But then, we get to the end, and suddenly there goes that valuable perspective. We know that Macomber dies a happy man, having discovered the meaning of manhood in his life in his final hours. In shooting the buffalo, he makes up for his failure with the lion (and even wants to take another crack at it) and feels a "feeling of happiness about what's going to happen" (4.17). But, most importantly, he frees himself from domination by Margot – a freedom that she clearly finds way too threatening.
That narrator, who was so helpfully insightful earlier, suddenly won't tell us what Margot is thinking. What is her real motivation for shooting Macomber? Was it an accident? Figure it out yourselves, says our narrator.
The only think we do know is that Macomber is dead, and Wilson is taking this opportunity to cruelly torture Margo by implying that she just might have murdered her husband. Many who have read this story simply can't seem to agree on whether or not she meant to kill Macomber – some definitely believe she was driven by hatred and vengeance, while others think she meant to defend her husband but wasn't such a good shot (it's not like she has a ton of hunting experience). Hemingway – or the narrator, we should say – does tell us that Margot "shot at the buffalo." That narrator has told us the truth before, so why would he now say she "shot at the buffalo" (4.42) if, in fact, she shot at Macomber?
In the end, the real question is: what do you believe? She is either a henpecking wife who, despite all her faults, tries to protect her husband; or she is a henpecking wife who is also a murderer. Awesome readers, it's up to you.