The issue isn't about compassion. I think we all want the suffering to meet a peaceful end. But what worse is that the crux of Buckley's argument is that the Pope is no longer useful (wrong on that, anyhow) and therefore, his continued existence is no longer needed.
He's not saying anything of the kind. Maybe you should read the article again.
You bring up an interesting point. For me, it isn't that JPII is without use, but I do think that a young and mobile Pope would be even more useful. Of course, I have my own opinions of what sort of stance the new Pope should take and all of that, but the point is that JP has served the Church well for 20+ years and, I think, take a rest. I don't mean that he should resign, but I wouldn't be sad to see him pass.
The Pope understands the deep theological reality that suffering is redemptive. He is uniting every moment of his suffering and dying with Christ. Suffering in this capacity is not worthless rather it is the greatest act of love that an individual can offer and when united to Christ has profound redemptive value defeating evil in the world. The Pope has prepared for this moment his entire life and embraces it out of love.