CO2 can be converted to methane. It just isn't profitable to do so yet. After the fossil fuels are depleted, it will be a viable niche for storable energy where renewables aren't practical.
Once fossil fuels run out, most exclusively-fossil-fuel-based activities will simply cease to be economically feasible.
That doesn't contradict your statement, of course. But in the long term the fossil fuel niches will start looking more like today's rocket-fuel niches.
Methane synthesized from excess renewable power can store that renewable power for years, handily fixing the whole "Sun don't shine every day" problem.
It's durable energy storage and can be easily moved around like liquid fuels.
It also would remove CO2 emissions from things like airplanes, which won't be able to be battery powered in the near future, and could renewably replace chemical feedstocks in lots of industrial processes.
But this requires immense industrial capability, probably some serious innovation in absorbing CO2 from the atmosphere because that's basically an unsolved problem right now, and a massive oversupply of solar power which cannot happen under market systems because nobody builds infrastructure to sell power at below market rates.
