Indeed, it is doomsday porn, something not uncommon on television and I don't expect any of those scenarios to happen any time soon but it shows that our modern civilization doesn't need that much to come to a halt, even if only temporarily. I wouldn't be too bothered about a three month power failure here; there are options enough to survive, but to major cities; something like three months can be lethal. But it would surely solve their rat and stray cat problem.
The more technological we become, the more vulnerable when losing that technology. Take the US army as an example. There is no doubt it is the most technological advanced army in the world but, as China knows very well, crippling it back to a WW2 status doesn't take much more than eliminating their satellites.
The same goes for our societies: while a shepherd in Afghanistan will barely feel the effects of modern technology being halted, in the civilized areas, people will drop like flies.
A lot of "ifs" for such a scenario to happen indeed but at least it should awaken us to the fact that life depending on food-chains for survival can have consequences.