Undead Labs is hard at work on Sandbox mode, which will be introduced with the next DLC's State of Decay : an update on their official blog , developers have explained how this will work.

The underlying concept of Sandbox mode is to provide a realistic scenario, not vinvolato to a story mode: what is going to happen is that, once we have started raiding resources from the Valley homes, these do not appear and will collapse and then getting some more, until you get to the point where we realize that the area no longer has anything to offer for our survival and that we will soon be overwhelmed by hordes of zombies.

At this point there will remain only one possibility: try to restart an old van seat at the edge of the penalty area, fuel and recovering missing parts to fix it, and then move into a new area that nobody has yet plundered but in which zombies are even more hungry than the previous ones. Once started the van we can take with us only some of our companions, so we will have to make a choice on who will accompany us, after which once turned the ignition key a loading screen will lead us into a new Valley, basically a Valley like the above in which we again try to survive until this drained of all resources and we will have to move again.

For now this is all that has been revealed, but the developers promise more information in short: If you're a fan of this particular title, continue to follow us for all the latest news.