You would be betting wrong if you think the majority of educated keepers feed live over prekilled or frozen thawed. Yes, many keepers still offer live prey as a rule, and many of them do it for the 'show' not for any real benefit to the snake. A few of us have select animals that simply will not eat f/t or p/k prey - there are some snakes that simply refuse to be switched, but they are typically wc specimens or a handful of finicky eaters. If you are familiar at all with wild caught imports, you will know that most come in with scarrs of one sort or another if they have any age at all to them. So yes, it does happen in the wild, fatal or not. No amount of supervision can prevent a bite. The fact of the matter is that it all happens too fast for us humans to interfere until after the fact. It is well documented that rodents can and have maimed or killed pet snakes - especially in instances when the snake chooses not to kill or eat the prey animal.
In the early years of my keeping snakes (I started 13 years ago), I only fed live because there weren't really any other options that I'd heard of at that time. Then one of my boas was bitten. While it wasn't fatal, it did swell and require treatments - daily shots as well as a topical antibiotic cream. For the record, no snake likes getting shots and it's at least a two person job, even for a snake as small as a corn snake (I've also had to administer injections to a 4' grey rat snake I had) much less the obstacle of giving a 6' boa her shots. After that first bite to my boa some eight or nine years ago, I started prekilling my mice and rats because it was unheard of for the average keeper to have access to frozen, shipped prey items...a wonderful advancement for the modern keeper. When frozen prey became available and more widespread, you quickly saw me changing over to it. The convenience of having prey items on hand as well as the health benefits to the snake far outweigh any thrill of watching them kill their own prey.
Raven