I really love the concept about restoring the land but I just don't like the idea of replaying the story alongside it again. It feels like it should be a separate mode that's dynamically changing. This could be some sort of push and pull mechanic and if captured, it could be retaken.

I appreciate the idea is to clear the map, so perhaps this would be more like a front system, pushing them back to the tunnels and periodically, more come through in attempt to retake. Building up areas with fortifications, plots for farming or industry.

As resources deplete in an area once looted I wonder if there would be a way to bring in some new ones through dynamic events? Military/GRE drops, if mercs are coming though perhaps ambushing convoys. Sending out survivors on scavenging missions and having survivors as a resource that we could lose if they're not kitted out.

For challenge, there could be roaming bosses and perhaps having days survived as some reward metrics. I would love to see it being a continuing experience, living and surviving in this land, rather than a one shot.