I'm probably going to be the only American to say yes. Admittedly, I'm not familiar with his exact medical situation--whether he is about to die or has some terminal cancer that may take a year or more to kill him. I do firmly believe in releasing anyone close to death, however. There is no benefit to keeping someone in prison at that point. Prison is primarily about individual improvement and the improvement of society. A man who is about to die has no further "moral" gains to be made from prison, and nor does society have anything to gain by keeping him looked away. He certainly is not a threat to others at this point, and that he would gain far more credibility as a "martyr" among those who believe him innocent had he died in prison makes politically (at least geopolitically; maybe not for those who want the SNP to win reelection) the move also the correct one.
Meh, I'll prepare to be shouted down by bloodthirsty vengeance-seekers who think he should been put before a firing squad.
Considering what he done, he definitely deserves it.