Killy did what he was assigned to do: Find someone with a Net Terminal Gene and get them to connect to the NetSphere in order to bring some semblance of order to the insane world.
Of course, after the kid in Volume 1 died, there basically weren't any living ones left. But somehow Sanakan & Cibo (with some help from that genetic data from Toha Heavy Industries) created a new one.
Killy had to go to the edge of the City to raise the child (poor kid, being raised by Killy. Probably can't even talk) because there was one area as yet uncorrupted there. At the very end he was making his way back in to find a functional terminal. Judging by NSE, he completed his mission successfully.