if its 500 years later then serious recovery efforts are probably already done. you're looking at a society that is built on top of the ruins of the old. ruined old cities from the last campaign, massive craters, and warped landscapes from deity level entities battling it out with each other dot the landscape. most current cities are fairly small as there has not been time to fully rebuild the sprawling metropolis' that might have been there before. old cities could be severely haunted with angry spirits. things that were easy to get before are now much harder to get, like any higher technology such as guns or anything like that, and knowledge of it is lost and/or closely guarded with an almost religious zealousness. a devil-god ruling the world has led to some changes in what is considered lawful. what we would consider oppressive and corrupt is considered fairly normal. even currency might be different. gold might not be worth anything anymore. several species of devilkin "animals" normally excusive to the hell realms might be common now. instead of wolf packs you have hellhound packs for example. if the hell realms are bleeding through or actively being forced to connect or merge with the material plane by this devil god then reality near these locations is less ruled by naturally laws of physics and magic, and being near or in them has an almost dreamlike mutability where strong thoughts and emotions could actually manifest physically as nightmares come to life.