Complex sentence: Sercey did momentarily reconsider, when the British ships declined to attack the temporarily disabled frigate "Forte", but eventually withdrew completely, retiring to his base at Île de France (now Mauritius) where he learned of his error.
Split into simpler sentences: Sercey did momentarily reconsider when the British ships declined to attack the temporarily disabled frigate "Forte", but eventually withdrew completely. He retired to his base at Île de France (now Mauritius) where he learned of his error.