Most martial arts instructors generally advise students to disengage from violence whenever possible, only using their "deadly skills" as a last resort. There are lots of reasons for this -- some good, some bad, some philosophical, some practical -- but is it always the best or right advice?
no its not the best or right advice.....for the student... Generally it is the safest for the instructor in an age where lawsuits get flung as far and all encompassing as possible.
So instructors will say what they need to cover their own asses first, and then protect their students second.
to be honest you should never engage an opponent unless there is no safe way out... turning and running may not be a safe way if you are out of shape and turning and running is simply going to tire you out, or if you have people with you who can not flee, or if the opponent has a gun, or any number of possible circumstances.
once you have decided that engaging is the best route, then you absolutely should not disengage until the threat has been eliminated... what does that mean?
well if you punch a guy then run he might easily be able to recover and get you and beat you. lets say you work a perfect technique on an opponent and break his leg and start to walk away and he pulls a gun out of his pocket and shoots you... all perfectly reasonable examples of disengaging to soon from a confrontation... do you have to kill the guy? Nope, very few circumstances do I think merit killing an attacker, and usually those will be when multiple attackers are involved. However you should not disengage an attacker until you have rendered the situation safe for yourself, or another attacker becomes more dangerous and you have to deal with them.
I personally think to many people say run away if you can no matter what... WRONG.. only run away if its the safest option for you... but how do you know? You have to work on your environmental awareness skillset. I think people with sheltered lives have trouble with this as oppose to those that grow up in bad neighborhoods. You can learn it, but you really have to want to practice being safe to make it a part of your lifestyle.
there is no easy answer, but to paraphrase something Ed Parker said "I would rather be judged by 12 of my Peers, then carried to my grave by 6 of my friends"
If I make a mistake I am making towards my safety not the safety of my attacker/s