I would be really surprised if the necrotizing fasciitis was related to his liver failure
Obviously, the alcohol comes to mind, but it could be a lot of other things, just probably not "the spider bite"
The Brown Recluse bite led to the Necrotizing Fascitis. While they removed a non-trivial amount of the flesh and muscle from his arm, there's really no way to 100% contain the spread of the venom and mitigate the resulting damage, especially if it's internal and not detected early on in the process.