"Wow... it's almost like they didn't have redundant fibre down there too, and that nobody was monitoring or noticed that their fibre strands were dropping off one-by-one...."
It was possibly the cable from the exchange to the roadside cabinets - I woulndn't expect them to be redundant, especially if it is an x-PON type system where there is only passive optical splitter/combiners in the cabinets.
I can also tell you from personal experience that the time between one bitten fibre and 8 or 9 can be very short - like a matter of seconds - it all depends on exactly how that particular rat goes about the job. If it eats around the sheath first and then follows up with a chomp at the kevlar strength member in the centre of the cable then it's going to take out more than one at a time.
The other aspect to consider is that if, as I mention above, there is only passive components at the far end of the cable, there is nothing capable of reporting a signal loss. As for loss of the back channel signal back at the exchange - is the cable cut, or have the customer's modems just shut down due to a power cut?