Real Graves is found alive, but he is really not well. Captivity and torture broke him - think something similar like prolonged exposure to Cruciatius like Longbottoms - and he is not really in any state to be left on his own, let alone go back to work. Maybe he is barely responsive, maybe he is mentally unstable, your choice. Healers really don't know how to help him and since attitude to mental illness isn't that good, some caregivers mistreat him or at the very least neglect him. Tina, who is one of the people who visit Graves regularly notices and is having non of it. She volunteers to look after him herself.

After a while Newt comes back to New York, maybe bringing his finished book and also his case. Some of his animals escape, again, and one of them is found cozying up to Graves, who actually looks happy and is interacting with the animal. Animals help Graves to emerge from his shell and ground him in reality. So Newt takes him on the tour of his case and let him help with animals and slowly Graves gets better.