Complex sentence: Durandal announces his intention to depart the "Marathon" to take over the Pfhor ship, but before doing so, he reveals that Leela was never completely destroyed, and the freed S'pht have released their grasp on her.
Split into simpler sentences: Durandal announces his intention to depart the "Marathon" to take over the Pfhor ship. Before doing so, he reveals that Leela was never completely destroyed, and the freed S'pht have released their grasp on her.