Sonny impressed on us very heavily the notion that you can never take anything for granted, and that being within range of your opponent was always dangerous. Always. Even after what might seem a 'kill' strike, never ever let down your guard or stay in range.
Also, from the other perspective, just because you got hit does not mean you cannot strike back if your opponent is having their brief moment of glory and forgetting momentarily where they are ..... If they are in range, strike them. (Which reminds me of Rory Miller's admonition (paraphrasing here) - Don't die just because you think you ought to, keep going until you are actually dead!)
It has been said that the only real 'stopping' strike guaranteed to end a duel immediately is a decapitation, so best to always be sure of range and keep fighting whether it's you that gets the first hit in or your opponent.
Below is a link to a great article looking at accounts of historic duels, targeting, and the centuries (more?) debate about the relative efficacy of cutting/slashing vs thrusting.