If we can’t survive without fossil fuels, we’d definitely be in trouble very quickly, given how soon they’d run out if we are unable to substitute something else in their place.
Fortunately the fact they can be made in the first place means we almost certainly can substitute something else, even if we have to make that something ourselves.
Nature wasn’t trying. The pressure, heat, and chemical environment that turns plants into coal, oil, and gas can be tuned to make the process much faster if desired. What’s the functional difference between 1kg of coal and 1kg of charcoal, for example?
And we can also extract CO2 from the air, pass it through the Sabatier process to get methane, then do more chemistry to get long chain hydrocarbons. Musk is planning to do this for his rockets.
Fortunately the fact they can be made in the first place means we almost certainly can substitute something else, even if we have to make that something ourselves.