If our motor vehicles were redesigned, made very small, low profile, with lightweight aluminum honeycomb frames, composite windfairings, etc. they might get up to 1500 mpg. just like this SAE supermileage vehicle:

This is optimistically 50-times the fuel economy of current sedans. Petroleum reserves could be extended 1750 years into the future. It would be interesting to find out how a solar-gas-electric-hybrid of the same size would perform, and if materials such as aerogel could be used to lighten their structure further. Such a car might cost $100,000 or more. A more economical vehicle might be a motor-assist bicycle with a 1-hp engine that gets about 400 mpg. In widespread use such vehicles would extend petroleum years to about 500 years in the future.

Given these numbers do you believe that we will have liquid fuels, or even a major transportation sector, in 1000 years? How about 2000 years? Global trade isn't possible without the ability to transport goods. Of course I could state the obvious:

Things will be very different 1000 years from now!