In the mid episodes, Safu's grandmother dies. Safu receives the remaining personal items, but the knitting needle she kept (the counterpart to the one she gave Safu) is missing. The second needle is what Shion grabs onto when climbing the mountain of dead bodies, which means Safu's grandmother was simply dumped off with the rest of the corpses.
Let's not forget the fate of the slumdwellers who are dumped into the room with the dead bodies - if any of them survived the fall like Nezumi and Sion, they are trapped down there with no food or water, surrounded by corpses. Logically, that would lead to rather desperate circumstances.
Nezumi comments in the first episode that 'living humans are so warm'. How long had it been since he touched a living person, and how many corpses had he touched since then?
Britain no longer exists in this world. Just how bad was this world war that it had wiped a powerful nation off the face of the Earth?
More like every nation. If you remember the fact that there are only six inhabitable places on earth you get a feeling for how bad it was.