a) diamond city is dope

b) nuclear war is extraordinarily underappreciated. like 0.3% of the former population is dwelling in a tomb, there literally haven't been enough people to clean up the trash and loot all the stuff. the fertility rate and life expectancy are rock fucking bottom. and fallout is optimistic about what humanity could do after global thermonuclear war. most analysts are going to be surprised a viable population survives the collapse, fallout, and famine at all.

c) i think the fire and radiation would put a pretty severe damper on the capability of natural processes to overgrow and degrade the ruins---which also have shittons of metal and concrete in them which have a life expectancy well over 200 years. ecological collapse will have fucked over the termites molds and bacteria so now a structure that should've rotted might stand up decades longer

d) the energy/powerlines stuff is waved away by miniature modular nuclear technology. a tiny fission/fusion reactor could keep a light on a loooooong time, though any lights people weren't actively replacing should be out