I am sure there are several hundred years left of Methane under the Earth.
I guess, it partly depends on how badly you want the stuff and how much you are willing to pay.
Perhaps if Natural Gas was reserved for house holds, Quarry Vehicles, construction vehicles, large HGVs, heavy trains and ships were made to run on Methane, then most smaller vehicles could run on battery power. What is currently being priced out of the market is Methane for electricity production. As less use is made of Methane, the price should come down.
One thing which almost certainly, should happen, is they should imprison the Methane speculators.