Kuma left behind all of his memories immediately prior to his operation, which Bonney is currently looking at. What's weird though is how Oda chose to offscreen Kuma's backstory. I think this is because Oda plans to have Bonney expose S-Bear, the Kuma clone, to the memories of the original. This will effectively bring Kuma "back to life" since his clone is receiving all of his past memories. Bonney may then also age S-Bear into an adult.
