Because divorce is a sin, while Michael had apparently justified in his mind that she was already dead, so therefore he was not murdering her, and that the only reason he could not already remarry his new lover was because he lacked a death certificate, not because he still had a living wife. I don't see how else you can explain his actions.
Her long-term friends (before Michael) testified that she was very Catholic in her beliefs and wouldn't want to die.
What rubbish. She did not regulary assist at Mass as an adult, and clearly used birth control prior to her massive weight loss which ended her normal fertility cycles. Her parents are big liars and a total disgrace to the side of good in this fiasco, who expressed theological nonsense such as allowing her to die would "lead to the damnation of her soul". Nor were they devout Catholics. "Today, the Schindlers say they don't attend church as regularly as they once did." (http://72.14.203.104/search?q=cache:0lABcnrB2rwJ:www.centredaily.com/mld/centredaily/news/7104920.htm+%22Bob+and+Mary+Schindler%22+%22attend+Church%22&hl=en&gl=us&ct=clnk&cd=4) There is no devotion at all from those who think Mass is merely an option.
I read the article you posted. What that article has failed to get across to you is that Mary Schindler has been a very faithful Catholic, despite the irregular attendance of her family. Many people have lapses of faith at one point or another, so for you to condemn the Schindlers in this area is, IMHO, not in line with the parable of the Prodigal Son.
Also, I don't know where you've gotten this idea that Terri "clearly used birth control prior to her massive weight loss which ended her normal fertility cycles". Unless you have a source you can cite for that, I think you are just speculating.