If we're not burning petroleum for heating/electricity anymore I imagine our reserves will be enough for thousands of years of roads, chemicals, synthetic materials, etc. By then we'll have developed alternatives, if not sooner

I think that's wishful thinking on the timeline and a very hopeful outlook for technology to save us. It also doesnt answer the question of if some of the byproducts are only useful for burning. If I remember right, gasoline was originally considered a byproduct.