And just decimate 70% of the population whilst we have an infrastructure that required billions to function and not self-destroy ?

Nearly all of the current global industrial lnfrastructure including energy and military require proper, careful maintenance in order to avoid disasters. Nuclear powerplants and nuclear waste disposal sites need to be connected to a wider grid and kept in working order at all times. Ammunition depots require maintenance or else they either risk leaking hazardous materials out or ignite and fuck shits up if anything happens to them. Decay of the very gears that keep our civilization running has only been kept at bay so far because of the continuous effort of the global capitalistic trades everywhere to produce and maintain production. Abandonning all of that infrastructure due to an universal self-extinction event would only leave on the planet a incredible number of ticking time-bombs everywhere. Life on earth would be permanently affected and poisonned by it. I get that human-activity globally need to be put to a halt for the biosphere to adapt and hopefully regenerate, but as is, without a proper dismantling and handling of all of our now-obsolete infrastructute and components, we're only going out irish style and leaving everything else a nice nasty fucking gift behind.