Complex sentence: Danny, Wendy, and Halloran (who had only been stunned by the attack) escape to safety as Jack runs to the boiler room to sacrifice himself by allowing the boiler to explode and destroy the Overlook.
Split into simpler sentences: Danny, Wendy, and Halloran (who had only been stunned by the attack) escape to safety. Jack sacrifices himself by allowing the boiler to explode and destroy the Overlook.