What's the intent of your fail safe? There are setups to run dual power steering pumps that would allow you to limp back if one pump fails. As far as the ability to steer of a line blows you're SOL as there's no mechanical linkage between the steering wheel and the axle on a full hydraulic setup.
You can still steer a full hydro in the event of of steering pump or engine failure. steering effort is difficult but doable. If your concerned about hose blowout, you can carry some #6 or #8 AN/JIC caps with you. In event of blowout, screw some caps on, replenish some loss of fluid and drive off the trail.
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