Complex sentence: If Tethys had been colder and more brittle at the time of impact, the moon might have been shattered, and even if it survived the impact, the topography of the crater would have retained its shape similar to the crater Herschel on Mimas.
Split into simpler sentences: If Tethys had been colder and more brittle at the time of impact, the moon may have been shattered. If it survived the impact, the topography of the crater would have retained its shape similar to Herschel Crater on Mimas.