Your last sentence (italics added by me for emphasis) is not fair, in my opinion. I can't judge prison conditions worldwide, but Taiwan is not a serious human rights violator. Does the USA even have medical leave for prisoners? In the USA, people routinely die in prison while serving sentences for trivial offenses. An unpaid traffic fine gets you imprisoned, raped in the ass, beaten, and stabbed. A friend of mine is a an emergency room doctor at a major hospital here in Taitung, and he says that prisoners are routinely brought in (I've witnessed it myself) for tests when showing signs of illness, and that the guards actually do seem concerned about the prisoner's health. In America, I hear tales of prisoners dying in their cells because they are denied medication that they need to take regularly, and are almost never brought to a doctor until they're near death.
I wouldn't want to be in prison anywhere, but if I had to choose between serving a sentence in Taiwan vs the USA, I'd go with Taiwan.
As for whether or not Chen should be released, that's another story. I actually think he's served enough time for corruption and should be released, regardless of his medical condition.