A certain middle eastern sheik who was a big wheel in OPEC, his name eludes me at the moment, was asked this question about the worlds oil reserves running out in 30 years time. He answered like this.
The stone age did not end because there was a shortage of stone, likewise the bronze age did not end because of a lack of bronze.
The oil age will not end for lack of oil because there are still huge reserves yet undeveloped, and technical advances will see the dependence on oil diminish as the years go by.