I just watched a very interesting documentary on channel 4, One Punch Killer, highlighting the impact of one punch in three different altercations. All three cases ended with the death of an individual.
The documentary followed the consequences of their actions, two imprisioned for manslaughter, despite pleading self defence and one found not guilty and acting in self defence.
Either way their one punch ended in the death of another individual. As part of any proper self defence training, dealing with the consequences, must be part of the syllabus.