Final answer:
At least ten lifeboats went back to save survivors after the sinking.
Step-by-step explanation:
The question asks about how many lifeboats went back to save survivors after the sinking. Based on the provided information, it is mentioned that at least ten boats had been lowered, and between 600 and 800 passengers had left the ship. Therefore, it can be inferred that at least ten lifeboats went back to save survivors.