The oil might "just" run out, either way it was obvious to everyone that natural resource-based wealth won't last forever, just like in that Sheikh Rashid quote from around 1988:
"My grandfather rode a camel, my father rode a camel, I ride a Mercedes, my son rides a Land Rover, and my grandson is going to ride a Land Rover…but my great-grandson is going to have to ride a camel again"