Short answer
Recovery depends on how sick he became. If he had vomiting or diarrhea from the high fat and sugar, your vet likely provided supportive care like fluids and a bland diet. You'll need to follow that diet plan at home, usually for a few days, and gradually transition back to his regular food. Monitor him for at least 24-48 hours after symptoms resolve for any return of stomach upset or signs of pancreatitis, like a hunched back or persistent vomiting. Keep all rich foods, including durian, completely out of reach in the future.
Durian — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Very high in fat and sugar, and the smell alone puts many pets off. Small amounts at most.
The full verdict, portion guidance and serving notes are collected on the Durian food facts page.