Complex sentence: When the sergeant came back to his village, he returned to find a soldier with a letter of pardon for "Gauchito" Gil, which also said that the sergeant's son was very ill and on rthe brink of dying.
Split into simpler sentences: When the sergeant returned to his village, he found a soldier there with a letter of pardon for "Gauchito" Gil. The letter also said that the sergeant's son was very ill and on the brink of dying.