That's why the Saudis have for a long time extended their business, investing heavily in real estate and what have you. Oil will be gone in 100 years, the skyscrapers won't.
Using money to make more advanced development possible, that's investments. The Norwegians got it right IMHO - they put all their oil money back in the economy, and they are punching now way above their weight! They have about 1% of the EU population, but own about 10% of EU Companies through their investments. Bar any major catastrophe, or very stupid decisions, they will have a good life for generations to come, regardless of their oil futures.
The average Türk, except for the very upper-class, would be very happy to end the influence of the Saudis in their country.