With all engines out power for the hydraulics is either nil or extremely limited. From 37000 feet you would lose power to control on the way down as opposed to the miracle on the Hudson where sully still had some hydraulics as he was close to the ground.
Did they definitely say it blew up high? I did t read that
I haven’t heard anything definite yet.
Even if they lost all hydraulics, the pilots would still have had time for a “Mayday” call.
The missing Egypt Air plane is an A320, which appear to have a ram-air turbine to provide hydraulic power in case of loss of engines.