Well I was thinking we play this out on two fronts, the first is 2015 when the disease and conflict starts taking notice, and then the "present" of 2114 where survivors start trying to rebuild society with whatever is left. I had some ideas for a few of these factions such as 
Mountain Men (progeny of survivors who took to incest to survive and became mentally unbalanced)
The Reapers (people who went underground, occassionally popping up to kidnap survivors and put them in a fight to the death for amusment)
The Remnants (good intentioned survivors who wish to rebuild society)
The Curators (survivors who wish to perserve mankind's accomplishments, but don't give a damn about human casualties)
Or just general survivors