When the use of Gasoline is exhausted, then what?

If exhausted try to run your vehicles or life by lng or cng's.

i think that hydrogen from salt water to create eletricity

Being a citizen of US you need not worry because US has kept a huge reserve of gasoline in Alaska for future use and now they are buying it from middleeast. If the resources are exhuasted, one should develop (it is being tried) new and renewable energy like cottonseed oil in India and some other seeds are used in Brazil. Solar energy is one great potential to be tapped.

There are many substitutions now being research to reach equally the same as Gasoline's efficiency. Solar - efficiency and clean, but depends on Sun Hydrogen - very clean but dangerous due to easily exploded Bio Chemical - USA developed using Corn and Sugar. Some third countries developed using other plants for its oil production. Atomic Fusion - Still intact with bigger scale, not available for small scale usage. Thermal Heat - almost like Bio Chemical, but this concentrate on the heat compression. Rechargeable Electricity - It's new invention nowadays, the automatic refueling for longest usage. This is the most efficient and no leak on the usage. And another future tech invention, I think the last point is the possible intact for future vehicle appliance fueling system, the auto recharge over and over.

Wars will end.

veggie oil its natural resorce we can make that stuff 24/7. This is what we sould be doing now lol.

I don't think that gasoline will disappear suddenly. It will slowly become exhausted because it will become progressively more and more expensive to obtain. * People will vote with their wallets, or wheels in this case. We will note a sudden drop in sales of gas guzzling autos in favor of high efficiency cars or electric hybrids. Bike use will explode, scooters will multiply like tribbles, and bus ridership will take off. Little start ups working with alternatives like solar will get the kick in the pants they need to go nuclear.