People have been picking out Barb's casket for quite a while, but realistically she could outlive Chris. I don't think she is as frail as many people think, she lost weight and appears to have some possible neurological issues either from a stroke or maybe dementia setting in, but she is one of those mean old battleax women who somehow outlive everybody else. They outlive everybody who starts planning for their demise, possibly out of sheer spite. She's 76 and could probably go another 15-20 years.
Chris on the other hand is obese, lives a sedentary lifestyle, and lives on fast food. According to the Father Call, he was on medication for his cholesterol in his 20's. He can't be in good cardiovascular health. Who knows what other substances he puts in his body to grow a TRUE AND HONEST china, and what effects those will have on his long term health. I've read a few articles about studies that have found that people with autism have a shorter life expectancy than people without it. I've seen the average life expectancy listed at 36-39 years.
At the end of the day, who knows how long any of us have, but the "homeless when Barb dies" saga isn't a given.