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I haven’t seen this yet, but I remember a show from Discovery about this. “What would happen if, suddenly, humans disappeared from Earth”.
The bad news is that pets would be the first to suffer, specially the ones locked inside homes.
Curiously we wouldn’t have many catastrophes like nuclear accidents or damns breaking (at least for some time) because everything is very automated and many fail safes would engage.
The whole show took as base many cities that had to be abandoned in different ages. It was very interesting.