No oil =/= Mad Max Future
People would build farming communities and would attempt to protect each other from zombie biker gangs. If you want an idea of what human society would be like without oil, all you need to do is look back 200 years prior to get an idea. Yes there would be no oil to run the machines and 5 billion people would die, but human society would still be sustainable. The world proposed by this movie doesn't stand up to logical scrutiny.