The adults attempted to set up a system for the children to govern themselves, but it got bogged down and was never completed.Too many parents trying to make sure their own children got an extra edge lead to infighting and roadblocks.
The plague is still in full-force - teenagers will die. Mankind is doomed.It's depressing, but a possibility.
The sequel wasn't published because it included sexBecause most of the main characters are headed headlong into adolescence, with no grownups to keep an eye on them.
There are adults somewhere in a hermetically sealed building at the CDC, still trying to find a cureI'm sure someone thought of something.
The reason the virus spread so fast was because it was spread by childrenJust because the children were immune to the virus doesn't mean it couldn't get into their bodies. Plus, the plague could not have spread own if it really was as fast-acting and deadly as it was. Thus, we have a Typhoid Mary situation where the immune children unwittingly pass the virus along to adults.
The dead kids go to Everlost.