As a rough rule of thumb, the power loss below spec can still allow "airworthiness" if the cause is known (ie, a dirty engine or one with a worn compressor and not one with internal cracks) and if the power loss is reasonable.
Some maintenance procedures for military turbines allow one that fails power assurance (HIT check) by -10% torque to be flown (Black Hawk for example) , some even allow -15%.
Is a low power engine more likely to quit? Probably not, if the cause of the power loss is not an internal mechanical failure.
Is a low power engine less trustworthy? Not necessarily, but a dirty engine or a worn one is more likely to stall, and more likely to accelerate more slowly when called on for power.