This is an interesting question. On its face, it seems to be misleading in terms of the events in the novel, but a closer examination suggests some deeper truth.
The word "salvage" is significant here. It has connotations of loss and reclaiming something specific after experiencing loss. Also, the reference to "facing death" is vague, since Frederic faces death in numerous specific incidents in the novel.
One response to the question would be to examine Frederic's behavior after the battle during which he was wounded. He is surrounded by death, overwhelmed with it as he watches his ambulance crew blown apart. Hemingway's description of Passini's agony as he dies and of Frederic's desperate attempts to help him show the horror of death that Frederic experiences. The horror is further emphasized during Frederic's ride in the ambulance, as one of the wounded being removed from the field, when the man on the stretcher above him bleeds to death, his blood falling on Frederic, who is trapped below.
Yet after his own wounds are healed, Frederic returns to his unit to face death again, this time knowing the terrible nature of what awaits him. In doing so, what might he have salvaged? What had been lost? Not courage--he had not lost courage. By returning Frederic salvages some sense of control. He chooses his path. He cannot control the horror of war, but he can control his own actions in the face of it. Interpreting Frederic's actions in these terms is consistent with Hemingway's "code hero," a man who endures life and deals with its often savage senselessness through the strength of his own will.