The 747 had 4 independent hydraulic systems (one for each engine). There were still failures that took out all 4. What comes to mind is the one where the rear pressure bulkhead failed (due to a faulty repair), and the decompression took out the rudder and all 4 hydraulics.

The pilot no longer had flight controls. He desperately tried to control the airplane using variable thrust, but it just wasn't good enough, and crashed into a mountainside.

The fix was to add automatic valves in the lines so loss of pressure wouldn't bleed out the whole system.