Wait, is this bark you're talking about the bedding??
You don't save bedding.. you toss it and replace after a month or so and certainly don't use it for new animals. For a new animal you should be using paper towels or newspaper instead.
Your friend does not seem to know very much about these animals. For one, the snake was in the enclosure with another snake and breeding without him knowing about it. To hatch the clutch you need an incubator with a specific temperature and high humidity - usually one that's hooked up to a thermostat.
Also, I work at a zoo and we hardly any porous material (besides aspen bedding that is constantly being switched out) and everything in the enclosure that is decorative is plastic/cleanable except for a few kiln dried climbing branches for certain species.
Since you have a glass tank, get two hides like this or similar:
http://www.reptilebasics.com/hide-boxes/
Small water bowl and no decorations. Pitch the log hide, they are terrible for ball pythons anyway.
Mice are generally not chemically treated and usually don't get mites/lice.. I do not think that the animal died from what it ate. Unless you purchased it from a petsmart or a petstore that specifically labels their small animals as being vaccinated and should not be used as feeders.