Welp... i'll pitch something.
1. Quest: Survive.
How long? Not said. But will be automatically completed after 2-6 months. Modable in sandbox.
2. Quest: Are you really alone?
There will be unknown frequency right behind one of the well known ones. Something like 96,6 MHz - Not Only Static. In few days after completing the first quest there will be message from someone. They send you to some place in woods. You find there car with ammo, few dead guys, and a message for contacting.
3. Quest: Someone else.
Right-click to the radio with a message in inventory. There will be new recipe called First call. This will make same noise like pressing Q for 30 seconds, so better do it alone. after finishing. Quest will be finished.
This then unlocks new recipes, which will start dialogs:
- News?
They will tell you, how it goes. Just some random crap like "We found new home", "We found some food." "We loose someone.", I've got to kill someone I love.", "We're trapped." etc.
- Trade food
For growable vegetable they will trade non-growable fruit and vegetable, and maybe you can have trade for eggs, milk and butter.
- Trade Guns
Same as food, but for blades and blunts.
- Trade Firearms
You'v got the point by now.
4. Quest: Interference.
In 20 days after the finishing Quest 3 helicopter shows up. This time it will stays above player no matter if he hides or not and for extremely long time. Like for a day.
5. Quest: After the helicopter flies off, the radio will say that this was the army. The survivors you communicated with were recruited and you are on the recruit list too. If you want to join, go into some location. When you arrive, there will be parked military helicopter with rotating blades (nothing hard - Just draw the circle with spiral and you will be better than anyone else). You get next to the heli and... fade out.

"Against all odds, you survived to fight for another day"
25% chance of next text to be something like:
"With cannibals!" painted by blood. And ambient of your character screaming like eated out by zombies.

Just food for thought.

basically just a l4d styled gamemode? sounds neat, its like a challenge without the wanting to survive months, just the initial challenge