People have had terrible governments before, for most of human history in fact. I do expect global social conditions to deteriorate as climate change strains countries, but that's a far cry from the end of the planet.

As for global thermonuclear war, we could wargame likely scenarios and potential outcomes endlessly until the day it might actually happen. But anybody who tells you with certainty that one will happen in the next 20 years so there's no sense planning for the future (e.g. no sense building a power plant that will be used 20 years from now) is trying to indoctrinate you into a doomsday cult.