From a low hover you just add power and keep things level to absorb the impact. From a high hover the procedure does say it may be possible to regain airspeed and return to flight(the height necessary for this will of course depend on weight and ambient conditions). Once you get through translational lift you'd be fine on a single engine, about 30-40 knots. It normally doesn't take long to get through translational lift but being heavy will delay things. If it was an engine failure in this case, given the weight of all the Marines on board the crew may not have been able to perform the flyaway if they tried. Also I think they had trees in front of them obscured by the dust kicked up by the other two planes that already landed so attempting a flyaway would have been risky.