Am I the only one who thought that the other three crew members would each have a leg amputated so that they would need less air, food and fuel and could all return home as theee-quarters Martians like Anna-Jing?
I don't remember much about the story at this point, but here goes:
If the crew all had a leg amputated and then discarded, yes, there would be less fuel required for the trip home. However, if they decided make use of all that fresh meat via cannibalism or even auto-cannibalism, there would be no net reduction in mass, thus the required fuel would remain unchanged.
They could, I suppose, make use of Newton's Third Law of Motion and expel any waste in a direction completely opposite to their directional path for a bit more thrust. The Waste Cannon 3000 springs to mind, but they might not have the components necessary to build such a device. I'd imagine they'd have a very elaborate waste recycling system onboard, so there wouldn't be much flotsam or jetsam to work with anyway.
Additionally, the human body burns through an enormous number of calories while attempting to heal itself. Any energy that might be taken in by the newly acquired food source would be more than offset by the heightened needs of the body. Even more so if one or more decided to opt out of the Consume a Fellow Crewmate Nutritional Plan.