A fat savannah monitor is an unhealthy monitor. It's very likely that it died from fatty liver disease. When normal feeding is abruptly interrupted, fat floods the blood and the liver is unable to metabolize it. Savannah's are little pigs and will eat themselves to death if you let them. They also tend to be lazy.
Bugs are a large part of their diet in the wild, so night crawlers or crickets and snails are good for them. They love to dig and it provides them exercise.
I agree that they make great pets. I took care of an adult male for about 9 months while a huge injury on his back healed. He was completely untamed
when he arrived in a plastic crate and smeared in feces.
I unscrewed the top of the crate and began washing the cage and him off with the hose, while talking to him. At first he hissed and filled himself up with air and would whip around when I got close. After about 15 minutes of talking to him and washing him i was able to touch him and within 5 minutes I picked him up, and by the following evening, he slept all night on my chest. He potty trained himself to go outside when i walked the dog. It just had to be a routine time, and the same area. If someone stopped to talk to me, he would display his penis. Talk about fugly.. I'm sure he didn't think so... (look one up on google)
When he was done with his business he'd go right back to my front door, and then to the garage where he liked to sleep in the day until the evening when brought him back in. I didn't ever put him back in the crate, or in a tank. Warm baths and glycerin kept him shedding and healed his back.
They love, Love, LOVE to be stoked ever so lightly.
I couldn't deal with feeding mice so I fed him a varied diet of beef-stew meat with calcium tablets shoved inside, skinless chicken with bones, fish or shrimp. I'd hold him while I got his food ready. After about a month if he wanted food he'd crawl right up on my chest. Sometimes I'd take him outside and let him dig around for bugs.
He'd hiss a bit when groggy, until he figured out it was me waking him up.
He never bit me on purpose, but came close when I had his meat in my hand, leaving me with a half dozen barely bloody scrapes a few times.
He didn't have trouble with the dog or cat. He was only interested in what they'd been eating, otherwise they were speed bumps. It was a sad day when he went to back to his owner.
Savannah's are great pets, and I'm convinced they only bite out of fear, or possibly mistake you for food. You don't need to start with a hatchling or a young one, but I've heard males are more pleasant. Parasites can be killed with medicine.
I have an iguana now and they are much harder to tame, developing trust for specific individuals, whereas the savannah seems less particular.
Crocodile monitors are in a whole different category.
Please buy unwanted lizards from craigslist, boards, etc., rather than from the pet store, and spend time researching the lizard's proper dietetic and health needs. There is no reason these animals should not live 15 or more years. http://www.anapsid.org/