post-apacalyptic is a hard era to do. i disagree that people will have to buid from scratch, let alone the shack type houses of ENDZONE. there are so many scenarios that could happen to make it challenging for a game developer to decide where to start. the survivalist and prepper culture has a huge following now. i do think a game from that idea could be a success. it would have to have more options for what might cause the apacalypse. most games are geared from zombies and the fighting aspect.
i think if a game was developed carefully with the right options, the prepper community might pick it up as a learning tool. an option to pick between pandemic,weather disaster<ice age or gobal warming>, natural disaster< hurricane,earthquake,etc>,wide spread electrical outage, or maybe a govern break down or war situation< terrorism,religeous war,anarchy>. now give the player options of starting skills and different supply scenarios or as they call it a bugout spot. how these start choices affect the game and survivability of the player would become the training or learning tool for the survivalist communtiy or preppers. that woud be the selling point. i do think there is a market for such a game.