Only then would he know what he has done.
I hope his last blood-choked breath was excruciatingly painful. Die, bastard. Die.
I would say it's likely he did die instantly - he may have had a last few seconds of terror when the occupants of the car saw the Israeli helicopter coming for them - but once the rocket hit, it was probably all over in milliseconds.
No time for the brain to register pain.
However... Where he is right now, and where he will be for all the rest of eternity, I am sure he is in plenty of excruciating agony...