The saying has always gone "I'd rather have it and not need it, than to need it and not have it."
Being said, if it absolutely comes down to having to draw your sidearm, then there is obviously a serious threat that couldnt be dealt with otherwise.
Shoot to kill in self defense.
There is no telling what the other people might be jacked up on, I have seen cops FILL a guy with 30+ rounds and he was so jacked on drugs that even though he should have been dead, he didnt know he was shot(amazing thing the human mind) and kept going till he bled to death. Frankly, I carry 12+1/12/12 on me at all times, but if a guy on drugs can take that many rounds, I may not have time to reload twice, so shoot to kill.
I will say that there may be times that it isnt necessary to STK, say you had someone attempting to break into your home, but was no real threat to you. Although if he broke in you would be in every right to fire in self defense, a simple shot to the leg(s) would be enough to end that threat, unless he was armed.
In my opinion, if I was to draw my sidearm it means either I am grossly outnumbered and can not handle a fist fight, or the other person has a weapon of some kind(whether blunt force, knife, or firearm). In which case I will shoot to kill.