There are no viable replacements for fossil fuels for a tremendous number of uses. There is currently no plausible way that, for example, long-distance flights could run entirely off solar.

Your economic analysis of

> Oil is still used all over the place because it's cheaper than the alternative.

has no contradiction with prices skyrocketing. Fossil gasoline might get to $20/ or $50/gallon before it's more expensive than the alternative, and so on for everything else.

"Somewhat more expensive" fertilizer means more expensive food, which means starving people, which is horrible on its own, but which could also create a very dangerous political situation.

Also the risk isn't that we'll run out of fossil fuels, it's that continuing to use fossil fuels would cause so much environmental damage that restricting the supply, as horrible as that would be, would be better than the alternative.