We didn't have 7.6 billion people on the planet 100 years ago. 100 years ago in 1920, the world population was approximately 102 million. It's beyond naive to think that the systems from 100 years ago are capable of supporting the needs of 7.6 billion people. Besides the challenge of feeding people without rampant deforestation, you can say goodbye to most of modern medicine. The tech and knowledge won't go away, but the ability to deliver those goods and services will be greatly hindered.