Puppies chew because they are teething and they need something to stimulate their gums. You can't stop puppy chewing but you can make the puppy chew on his own toys instead of your house. If you have not bought a crate do so.
Crates are wonderful training tools for housebreaking and chewing.
Buy your pup some tough, indestructable toys. This surgery does not make the dog fat, stupid, less active. Plus a nuetered dog is less likely to roam, mark his territory, and is less aggressive. If your dog refuses to come when called you might have done something to make him afraid to come to you. At that moment your friend will let go of the dog.