He was at 27,000 feet and was bored so he decided to pull an engine on the young pilot flying
it depends what it means " he decided to pull an engine " . when he suddenly pulled back the prop lever to feather on a turbine producing cruise power ( so without first retarding the power lever to idle) it would be no surprise he cracked the reduction gearbox- and it maybe finally failed when he reved up the prop again. the exaxtly kind of damage would be interesting.
beyond that... he was bored and just "pulled the engine"??? with the result melting a 400000$ turbine ???
He was at 27000 in a king air?
Were they wearing oxygen masks?
???
In practical terms, at high altitude for a given IAS an uncontrolled (ungoverned) prop will over speed and the result can be the separation of prop and engine with disastrous results for the airframe.
hey! the only condition where the prop is not governed is the beta range/ground idle ( flat pitch) with the power lever on the pt6a.
best regards