Much needed diesel and heating oil will gel and become useless. Don’t count on fossil fuels doing any good to help anything at that point. The population issue will then take care of it’s self. There will be only small clans of those with the knowledge to survive on limited resources and without modern technology. We will once again be back in the stone age and maybe survive as a species to start all over again someday.
Unless there is catastrophic nuclear war, like a thousand or more bombs being used, I doubt we will go back to the stone age. However, we could easily end up in the iron age, perhaps something like 16th or 17th century Europe. I have read several books on the aftermath of war with electromagnetic pulse technology. Basically, only a few non-computerized vehicles usable in one case, and in another only horses and no guns, but arrows for defense.
I heard an interesting report today about scientists overseas working on producing kerosene like fuel for aircraft from CO2. So far the production is very scant, by the liter not the barrel, but they say no pollutants are produced in the manufacture, and if solar and wind are used, energy needs are met without producing pollutants. And the CO2 is waste CO2.