What will happen if all the crude oil over in the world

how long will the oil in the world last?

what is the next plan available to us? does it mean we need to use bullock carts after all oil over?
how far it is? we would return to ancient world?

To answer your question, There is enough Known oil for us to keep using Crude Oil for the next 100+ years but no matter what happens there are too many other alternatives to keep us going with electricity, Most people still don't count the fact that most of the world is still burning coal to get power. Then there's all the Renewable ideas coming into motion, you have Wind power, Geothermal power, Solar power and Magnetic(newer) power. Wind will always exist due to the sun heating the side of our planet facing it and the cooling of the dark side creates movement in the air, Geothermal power wont last forever but it can sustain us for the next 2000 years or so given our current power expansion rates, Most people know the power involved in Solar power can be more per day than humans use per year, and we're still just learning about magnetics, if correct Magnets are going to be the best way to transport electricity without causing harm to people mainly because Hydrogen is too explosive to think about mass transport

Natural gas, the next thing in line. Peak oil is around the corner, its just people realizing whats the best next step. we wouldn't go back to the 'ancient world' that is very unlikely. That isn't progressive nor constructive.
Lets not forget Coal being as abundant as well.
Anything "Green" like Solar panels are more of a liability then something beneficial so those are useless, as much as the 'Green' cars that are supposed to be efficient.
The batteries in those cars cost $2,000 which is absurd, we'd have to cut down several trees to print that money, let alone create the batteries, extract the resources to create it..its just very ineffective, an very destructive towards the environment.