I'm frankly not sure how this is relevant to a survival scenario where people may or may not be injured.
Anyway, the entire ISS is built around astronauts using their feet as anchors, allowing them to use their hands for work. Without legs, you wouldn't be able to do maintain your position while working in 0g, hence the challenges of spacewalking. There's plenty of videos where astros show how the top of their feet become calloused as they use them to lock in their bodies to the structure.
Again, look to Oscar Pistorius for a concrete example. The man has the same ability to move around as someone with legs, they're just made of carbon fiber. Many prosthetics have sophisticated articulation. We're a long way past the days of peg legs.
I fully expect an organization capable of creating the ISS to be capable of figuring out a way for prosthetics to be usable onboard. Put a bit of velcro on one of these, perhaps: https://www.youtube.com/watch?v=a2z8CE2vomY
I’d wouldn’t frame this debate as being about preventing people from entering a store, or going up stairs, or running in a straight line fast, or living a normal life.
This about a government choosing to spend many millions of dollars over 10 years to train this one person to do an insanely difficult job. So you can bet that any disability of any kind is going to be intolerable. They will pick people with 0 physical, mental, behavioural or cognitive disability. Bum kidneys? Out. Don’t react well to a fire or spiders or smoke? Out. Can’t solve the orbits question in less than 63 seconds? Out. Argumentative and not the best team player? Out. Sadly, this will also apply to any sort of physical limitation as well. It would be trivial to add some Velcro here and there, yes, but making the entire astronaut training circuit itself accessible, from everything like the 0g sim harnesses, which expect the weight of legs, to flight training, to the Russian centers, is sadly not gonna happen.
Anyway, the entire ISS is built around astronauts using their feet as anchors, allowing them to use their hands for work. Without legs, you wouldn't be able to do maintain your position while working in 0g, hence the challenges of spacewalking. There's plenty of videos where astros show how the top of their feet become calloused as they use them to lock in their bodies to the structure.