Fallout pnp zombie outbreak game idea

[Railak]

So I'm thinking of doing a zombie outbreak story using the fallout pnp game rules.
The idea obviously would be a one shot, but the main story has them starting in an airport, no weapons, usable things for weapons are going to be pretty easy to find. So the overall story is going to be that they have until Midnight to make it out before the military scorches the whole city.

The city is a made up one, still haven't thought if a decent name. It's population is about 50,000, and the airport is roughly in the center.
The normal zombies will be built as ghouls with no intelligence.
There will be a number of special zombie types, built using the various other races in fallout pnp. Like a brute that's built out of the super mutant.
Being bitten causes you to become a zombie, there isn't going to be any immunity to that, I'm going to use the disease resistance for how long it takes. Making and failing saves.

The main problems I'm having troubles figuring out. (Not really game mechanics)
1. How would they effectively contain the city? The military I mean, unless they erect walls/fence of some sort, but around a fairly large area is pretty difficult in a short time.
2. How to deal with a player dying, since it's just a one shot? Should I let them make another character or out the rest of the session, or helping manage the zombies?
3. Would it be better to actually have a story, or do it as a sandbox. Basically should I try making them go a direction I want them to, or allow them to figure it out on their own?

For the "story" I haven't really gotten past the airport in planning, aside from very basic city layout, and the fact that at midnight the whole city gets a very large bomb dropped on it, oh and it starts at about 4 or 5 pm in game.

[The Glyphstone]

Have the starting point be a mall or something. An airport could be a destination goal, but otherwise you will need to be extremely heavy handed in denying their ability to just leave in a helicopter or small plane.