The key is that some group would set up some form of government. My best guess is that governments which established rule of law, including respect for private property, would become more powerful relative to other governments. Technological progress would begin again.

Also, see what I just wrote to Roko about why resource scarcity is unlikely to be as a great a problem as you think and why wars and famines are unlikely to affect wealthy countries as a result of resource scarcity.