Done that.
Someone's heart was stopped. Someone I knew a bit, because he was in the neighborhood.
Called for help, tried to do something while waiting.
The guy lived for another 5 years and got to see his grandchildren.
However, some policemen told me for 15 minutes I could have had great problems for trying to help while help was coming... Got mixed feelings at the time.
Then, every time I saw him, he kept telling me I should have let him go...
But I regret nothing, plus I could have been charged if I had done nothing... not that it was the thing that motivated me in acting. Just that when something like that happens, you do what you feel is right... or you don't depending on so many factors. And if you do something, it doesn't mean it was the right choice either. Regardless of what you do, the result may be neither good, nor bad. It's just you're caught in a situation where you're screwed from the start.
Regarding Buffalobiian, people have to think that witnessing people in trouble, and passing by is very hard. Because remorse always strikes back.