Lightning strikes generally don't cause a lot of tissue damage (at least at the core vital areas, most of the "damage" occurs near the feet assuming the person is standing at the time). Most victims that are fatally wounded usually die of cardiac arrest. So, if there is medical attention within the immediate vacinity (namely, a defibrillator) the fatality rate decreases dramatically. Keep in mind these are all generalities, each case is unique and has it's own factors.