One of those moments when you realize that instead of merely repairing the holes on the underside aran panels of the sleeves on the sweater for the old lady in assisted care with dementia...you're going to have to replace the entire panel.
The yarn, an acrylic blend, is literally worn SO THIN in areas, that instead of yarn thickness, it's thread thickness. It will literally be quicker to steek the ruined panels out, and put in a reknit replacement. No kidding. How it's held together is just an act of God. No kidding.
I'll be making poor wages on this one, but it will be a mighty mighty mitzvah, to be sure.