Depends on who the person is I guess. I'm a firefighter do everyday we go to work with the possibility of risking our lives for a strangers. But if it was a certainty that I would lose my life for someone else's life...itd have to be someone I truly love.
I think I would save the person's life. I would have at least done something worth remembering and he or she will forever be grateful to me. I would also find peace and fulfillment other than leaving with guilt for letting another person die.