I'd save someone if they were in danger, I'm not one for confrontation but I do try to protect people. Also there is no mysteries to death once your dead your dead this isn't call of duty.
I do not see myself dying for someone I do not know. First of all, many questions come to mind. One thing, it could be a complete innocent small child. Then, on the other hand it could be a criminal that will take many lives if he or she continues to live. Not really a fair situation to be put in. I do not think I would, but I would feel a certain amount of guilt afterwards.
Not to be selfish, but I'd only do it for my girlfriend or my son. Maybe some of my friends. But I wouldn't do it for someone I don't have any knowledge of. Or for someone I don't even know exists. Just my thoughts.
If it was someone i was very close too, a family member or wife/girlfriend. Yes i would. I couldn't live with myself knowing i had the opportunity to save someone and failed to do so.