He switched places with the gardener. That's how he survived. Its left ambiguous whether seung chun and joo hee…
I think he does eventually get back his memories because he still had his spoon with him when they switched places. According to the grannies final rule anyone who eats with the spoon gets the owners memories. So if he had eaten with the spoon at any point his memories would have come back. They leave it ambiguous whether she recognizes him.