Oil will be worth more than diamonds
Look into the Petroleum Production Curve. It's leveling off. Many oil companies and countries are restating their reserves. They've been fudging the statistics of reserves and recovery for years. The Age of Petroleum is peaking. Enjoy it while you can, it doesn't matter, it is a finite resource. The discovery curve has peaked. Your kids will not look at petroleum the way you do. To them, oil will be worth more than diamonds.
Oh, and ethanol and hydrogen are not replacements for petroleum. It takes energy to make both. The energy balance ain't even close.