Explain what impact the controversy between the accidental and purpose killing of Francis Macomber has on the story.

The whole point of the story comes down to this last
page.  The question is, "Does Margot kill Francis on purpose, or is it, as she says, an
accident?"  In order to decide on the impact, you have to think about what Hemingway's
point is by the end of the story.  This story, like most Hemingway stories is
illustrating what we have come to see as the Hemingway Code Hero.  Francis hasn't acted
like much of a man/hero throughout the story.  He fails on the first hunting expedition
and reveals his cowardliness.  Margot doesn't respect him or their marriage.  But on the
second hunting outing, things are different.  Francis is finally becoming his own man,
and is bravely hunting the lion. It is is in this moment of personal glory and "grace
under fire" that Margot kills Francis.  Does she really do it on accident in a failed
attempt to save him from the charging animal, or is she suddenly realizing that Francis
is coming into a new understanding of himself and will likely no longer put up with her
behavior and control of their relationship?  Hemingway never directly tells us what the
truth of the matter is, but Wilson's reaction and Margot's comments lead readers to
question the veracity of her story.  It seems very likely that Margot feared for her
life (as she wanted to live it) and saw to it that Francis couldn't change anything. 
He, as the title of the story suggests, had a short, happy life -- he felt truly alive
-- for that short time in this final hunt.  He lived up to the ideal of the Hemingway
hero for those few minutes!