Complex sentence: The outcome of the battle was decided when Dara Shikoh's descent from his Elephant Howdah at the most critical moment of the battle, when his elephant quickly fled from the battlefield Dara Shikoh's troops mistook this event to indicate his death.
Split into simpler sentences: The outcome of the battle was decided when Dara Shikoh's descended from his Elephant Howdah at the most critical moment of the battle, his then elephant quickly fled from the battlefield. Fleeing elephant was evidence enough for Dara Shikoh's troops who mistook this event to indicate his death.