In the "Saw" film franchise a key event was John Kramer swallowing a casette tape covered in wax for it to be recovered in his autopsy. Could this realistically happen in real life?

Virtually any object small enough to pass through the pharynx may be swallowed. Items commonly ingested by children include coins, small toys, pencils, pens and their tops, batteries, safety pins, needles and hairpins – they are mainly radio-opaque. Food-related items such as fish and chicken bones are more often ingested by older children and adults and tend to be radiolucent. In adults dentures or parts from dentures can be swallowed accidentally and are reported in the literature.

http://www.patient.co.uk/doctor/Swallowed-Foreign-Bodies.htm

I think he was asking if the tape could be recovered without being digested, not if it could be simply swallowed.

Yup, the question really is whether or not something like a wax-covered casette could survive being ingested. hence, this question is still unanswered.

Paraffin (the wax often used in sealing home preserved products) is not digestible. That means that it passes pretty much unscathed through the digestive tract, which would make this feasible.

http://www.ochef.com/674.htm

https://en.wikipedia.org/wiki/Paraffin#Paraffin_wax

...recovered AT his autopsy.