On one hand many countries will invest in heavy industry, manufacturing, and fall back to fossil fuels.
On the other hand, economy overall should slow down and consumption of non-essential goods and services will drop.
I’m not expecting any definite answers or numbers, of course, just some food for thought.
Honestly, both outcomes seem equally terrifying. Either we wreck the planet faster through war-driven industry or everything collapses so badly that emissions drop, but at an enormous human cost.