Complex sentence: An estimated 20 survived the sinking and managed to survive a while by clinging to large pieces of wreckage, and all but two of these eventually succumbed to hypothermia, as did one of the remaining pair, leaving Henry Jelley as the only one of two survivors.
Split into simpler sentences: An estimated 20 survived the sinking and managed to survive for a while by clinging to large pieces of wreckage. All but two of these eventually succumbed to hypothermia, as did one of the remaining pair, leaving Henry Jelley as only one of two survivors.