As usual, the whole scenario is being overthought and all of these different variables are introduced. I haven't been in a post apocalyptic world, but from what is depicted in movies and t.v., saving someone who is paralyzed from the neck down is rarely achieved. The mortally wounded folks usually take a grenade and lay in wait for the bad guys or the creatures to swarm and then BOOM, but u can't pull the pin on a grenade if u r paralyzed from the neck down.
Sure you can.
A little string tied around the pin and the other end tied around your tongue.
Might take a couple of tugs if someone hasn't loosened it a bit.
Dave