Of course one critical system failure can bring it down, but it would have to be a serious failure. And the electrical system failing would have to mean that these backups all failed. If (and I mean serious IFF) the electrical system failed, than Airbus could be in serious trouble as all but 1 in production model uses this FBW system.
For them to lose all rudder control, and it not be structural would be something similar to the Swiss Air flight on the east coast where there was a fire in the avionics due to insulating foam. The Hydraulics last resort is simply that, its for basic steerage and nothing more.
Also, lightening knocking out the weather dopler is likely, however they would have had pre flight weather reports from CDG, as well as the information they had before it went down. The US weather network has serious storms in their flight paths. Also remember that almost all hurricanes that hit North America originate in that area of the Atlantic.
Compare the 2 flight decks. Airbus - A330 FlyByWire (FBW) with no stick, if the electrical and all backups fail all you have is rudder via the pedals. Electrical system is required to fly the plane hence the reason for the four fully
redundant electrical systems
Boeing 777 - newest model they produce only has 2 electrical generators, however they are independent and run all the time since its used similar to power steering instead of running a computer.
