The Limits of Piku'ach Nefesh: Is one to endager oneself in order to save others?

This past Sukkot, a group of young religious trekkers found themselves in the middle of a fluke blizzard in Nepal, a nightmare just recently revisited. Some sacrificed themselves in order to save others. Israeli soldiers endanger themselves for others - soldiers, civilians and even civilians of the enemy - as a matter of course. What is the Halachic response to such moral quandaries?