Does Alzheimer's Justify Divorce?

Pat Robertson upset a lot of people when he justified divorce by saying "If you respect that vow, you say `til death do us part. This [Alzheimer's] is a kind of death."

Dr. Amanda Smith: "To condone abandoning one's spouse in the throes of this mind-robbing illness is absurd," said Dr. Amanda Smith, medical director at the University of South Florida Health Alzheimer's Center in Tampa. "While Alzheimer's certainly affects the dynamic of relationships, marriage vows are taken in sickness and in health."
Source: Katie Moisse, Jessica Hopper. "Pat Robertson Says Alzheimer's Makes Divorce OK." ABCNews.go.com. 9/15/2011.

What do you think about this difficult moral question when a couple has to deal with a chronic illness?