I did something similar. Still am, actually, I just have let that game go by the wayside in recent months. I should pick it back up…
Anyway, I had a setting where the world of FR became overrun with undead, and Waterdeep was the last city left with living people. Their protections kept the Undead out, but the city was stagnating, running low on supplies, weapons and whatnot, with crime, disease, starvation and overpopulation running rampant. Anything Divine had been lost due to a disease that only attacked people of faith, thus robbing most gods of their power. And over the years, most high level npc’s have died.
So the party was supposed to find a way to leave Waterdeep and go out into the world, and find supplies, or stem the tide of undead, or find new cities, or whatever else they could and make way for the people of waterdeep. I gave them a number of options, places they could go to “Unlock” a new area and, if they succeeded in completing it, to “Unlock” new features for the city.
For example, there are some mines in the north that would have all kinds of weapons, armor and raw materials for the City Guard, because most of their weapons and armor are to the broken after years of fighting. But there’s an Undead baddie guarding it with his minions. There’s a forest filled with game and fertile land which the Undead seem to ignore, but it needs to be cleared out and fenced off. There’s a city to the south, Calimshan, which was completely abandoned and was left alone by the Undead, but no one knows why it was abandoned and, if secured, would be the perfect place to expand and add more room to alleviate the overcrowding in Waterdeep. The seas are overrun with undead pirates, but if that could be fixed, they’d have a good way to travel quickly. And the majority of the Undead seem to be coming from Icewind Dale, so if they could figure out why they are coming from there, the Undead hordes would lessen tremendously.
The point was that with each victory, the world becomes a little safer, but as they choose one area to fix, the other areas escalate. So if they choose food first, starvation will go away, and as a result some disease and crime will go away, but undead will continue to be strong as more weapons break, and travel by sea will still be impeded. If they choose weapons first, starvation, disease and crime will go up a few notches and the chances of a plague will increase, but the guard will be better equipped to repel zombies. If they choose the Sea first, they’ll be able to quickly and safely get to the other objectives, but starvation, disease, crime, and undead attacks will all go up, making a dangerous time in the short term until they can get other objectives done. And of course, opening up a whole new city would solve many of their problems, but add more if they do not have good travel or protections or supplies.
It’s very video gamey. But everyone seemed to be enjoying it.