For a historical perspetive:
The DC8 has a single main system of hydraulics powering the alirons, rudder, stabulator trim(the elevators are manually powered by the musles of the flight crew). Flight spoilers are powered by a separate electric hydraulic pump drawing fluid from a separate hydrualic resevoir. Sub systems off the main hydraulic system include landing gear, brakes, flaps, slots, nose wheel steering, ect.
In the event of a total hydraulic fluid loss, all systems are isolated from the cockpit. Flaps are lowered by remaining fluid and main electric hydraulic pump. Landing gear free falls and down locks are operated by a separate resevoir and the main electric pump. Also the slots are opened by this same system. Alerons are now operated manually by movement of the flying tabs. Stab trim is operated by an electical motor back-up system(the auto-pilot uses the same system to trim the stab normally). Rudder can be operated manually, but has a separate electric hydraulic pump and resevoir. Brakes are pressurized by air pressure.
So with fluid loss you have really lost nothing important. The airplane fairly easy to fly under the situation.
Ray