somehow, i doubt a north korean work camp is filled with "easy" methods of suicide.
North Korean Labour camps are not like our prisons, they are more like closed cities, He would still have access to the means to suffocate, hang, or gas himself with vehicle fumes (I doubt NK is much into emission controls) all of which are likely to be consistent with his severe brain injuries.
He might also of course have been water boarded for fun by his guards (IIRC it was the North Koreans who invented the wet towel trick) and they over did it. But I would be a little surprised at this. Usually, Westerners, and particularly Americans imprisoned in NK are valued as Pawns in the game and are typically discreetly traded for some favour once everybody has forgotten about them.
It is sad that his prank ended so awfully for everybody involved, But at the same time, he was never going to recover and the eventual outcome was probably for the best.
It is also worth noting that most Asiatic countries, not just NK, will take a very dim view indeed to foreigners who disrespect the authority of the state or do anything to disrupt their sense of social order. The reward for any such misbehaviour in any of them (Not just NK) is likely to result in savage legal reprisals compared to what we are used to in the west.
NK is certainly at the extreme end of the scale, but it should not be considered out of context. The legacy of the Qin Emperors concept of "Legalism" as a means to control the people runs strongly through all of them to this day.. :/