Lets say a vaccine was found in the game do you think the people such as hunters, looters, and all the crazies would want to bring back the old world or are they happy with how things are?   Do you seem them as trying to prevent the vaccine from going through?

they wouldnt prevent it, actually they would want it to happen so they can move freely and take rob and ambush more people

Other:

It's an impossible question to ask. Everyone is shaped by what they experience and how they change in order to cope with the aftermath of those experiences. So to ask this question is to ask someone to define themselves as another person. We can ask what we would do given our current personality because we can be objectional (given that we are driving the narrative with a joystick), but we couldn't ask a living breathing person of this fictional world the same question because they're always going to be subjectively driven.

The ones that remembered the old world would want it back because LoU had come out and they hadn't been able to play it in 20 years. They need the power back on and production facilities back running and making PS3s so they could relive the awesomeness of their video games.

I don't think it ever go back..at least not for a long time.

I think they will continue like they are, some will be hunters, and some will try to settle down and grow crops, but there will always be raids and wars between them.

but eventually the Europeans will arrive and establish colonies. They will wipe most of them out or move them into increasingly smaller reservations where they can peacefully continue their old traditions of killing each other.

Haha that sounds about right. 

The only thing that would have been accomplished by the fireflies was the death of an innocent girl.

As if a few doctors in a run down 20 year old hospital could even make a working vaccine, and even if they did they have nowhere near enough resources to distribute it around the country.

And as seen in the game, society has already crumbled and even without zombies the battle for resources, murder and bandits running lose would continue.

I think there will be a war, the military will never let the fireflies take control of the situation, and the fireflies will not just hand the vaccine over out of kindness, they will use it to rally an army to their cause and fight the military for control, so the vaccine would probably kill more people than it saves; besides, I don't think anyone cares about rules or society anyway, like Bill said normal people are actually more dangerous than the infected, too much bad blood between different groups, they will never work together peacefully.