Rashi on Genesis
לא נכנו נפש — supply the word מכת so that the meaning will be “Let us not smite him with a smiting of his life” — it means killing.
Sforno on Genesis
ויצילהו מידם, by first of all preventing immediate action by the brothers, committing an act which would prove to be irrevocable. This would have been the kind of thing Solomon had in mind when he said in Kohelet 1,15 that מעוות לא יוכל לתקן, “there are things so twisted that they are beyond repair.” He referred to matters from which sometimes the righteous person can also not be saved. One such example was the irreversible act of Reuven of having slept with Bilhah. Yaakov himself characterized it as פחז כמים, “hasty like water” (flowing downstream, something beyond recall).