I've seen some traffic light controlled junctions in Europe, a while ago I'll hasten to add, where out of peak times there is just a flashing amber, no light control of the traffic. But this is during quiet hours.
However I'd agree that in some circumstances road users can negotiate the roads during busier times without lights. I was in Liverpool several years ago when there was a powercut across all of the city centre, not a light was working. I wasn't a cyclist back then, but made an early dart imagining traffic chaos. To my surprise there wasn't, however I've got a feeling for everyone like myself who tried to beat the rush there was another person leaving the drive home "for later" meaning the rush home occured over a much longer time period, so although anecdotally traffic lights going down doesn't cause the congestion that would be expected, when they are down through faults it is a short term expediency that people have to live without them. Given a week of no lights I'm not sure the same courtesy would still be alive!