Abiotic oil is a pretty well developed theory. Lab experiments have show that temperature and pressures present in the earths core will form hydrocarbons from carbon and water. There's also all the extensive work by Gold on the deep hot biosphere. Also, the entire atmosphere of Titan is hydrocarbons for example, so it's not like hydrocarbons need life to exist. However, abiotic production is perhaps a few billion barrels of oil globally a year. Not close to enough to sustain our current civilization, but enough to try again in 10 or 20 thousand years.