OP here: I was referring to fossil fuels as things we burn to drive automobiles, airplanes and ships, or to power electric generators. So yes, petroleum will continue to have its uses, just not power. (Although my ten year timeline was hopelessly optimistic, I admit.)
Modern medicine relies heavily on petrochemical feedstocks (derived from fossil fuels.) These are used to make plastics, solvents, reagents, packaging, and some pharmaceuticals Many of these materials currently have no scalable, cost-effective substitutes.