Complex sentence: The original plan had been to leave a shore party on the Antarctic mainland while Worsley took the "Endurance" northwards, and there had not been the expectation that the entire expedition would live aboard the ship in the long term.
Split into simpler sentences: The original plan had been to leave a shore party on the Antarctic mainland and Worsley to take the "Endurance" northwards. There had not been the expectation that the entire expedition would live aboard the "Endurance" in the long term.