The end of Gas does not result in such a scenario.
Just to make this simple, in the movie it is stated that the end of Gas meant the end of power and electricity. This was ridiculous as you there are many ways to get hydrogen out of things we grow naturally, and we all know hydrogen can be converted to electricity anyway using fuel cells. Yes it's complex and expensive, but the mere fact that electricity can be produced from hydrogen using a fuel cell means that if "Gas", aka "Petrol/Fuel", runs out, we still can use biomass, use they hydrogen from that using fuel cells, and bam, you have power. In fact, even vehicles can use this.
Vegetable Oil even, you can get hydrogen from that, and technically using a fuel cell in a vehicle you canf ill a tank of vegetable oil and run your vehicle off that. Biomass Fuel FTW. Movie was good, but ridiculously not researched enough before thinking up the ideas.