Though it's true that only 1 billion people are sustainable without oil

---It's also true that using wind and water power and solar power might replace oil for many or even most uses here on earth.

If that happens oil can still be used to make plastics which for now cannot be made without oil. Also lubrications are still mostly made from oil too. So, most or all mechanical things need oil of one form or another to reduce friction so things mechanical don't overheat and freeze up permanently.

So, oil will always have it's uses, so it's better for us to convert to other energy sources now so we still have if for plastics, lubrication and other uses.

With the new types of batteries that people like at Tesla are developing it might be possible to charge a Farm tractor's battery through solar cells there right at the farm and even have several sets of batteries charging on sunny days and replacing those rechargeable batteries as needed to continue farming on your electric powered farm tractor. However, this might only work when there is enough sun.

However, if you had wind chargers combined with Solar chargers this might work as long as there always was either wind, sun or water power (rivers) nearby to charge your farm tractor's batteries.

Electric motors are more powerful than diesel ones. This is why you see Diesel Electric Train engines a lot. So, the most powerful Train engines are Diesel Electric Hybrids already. So, if you had a farm tractor that was a plug-in hybrid like a Prius or other hybrid is, when you had solar or wind or water power you would use that, but if it was cloudy or not windy you could buy diesel or gas and run your farm tractor worldwide that way.

This likely is where all this plug-in hybrid stuff is really going in the long run. So, you have multiple (at least two) energy sources to make it more economical as long as the electric motors can keep the mud and dust from farm lands out of them and are made tough enough for the bumps.