It's what he wanted.
Casey Peretti came to Oakdale to work at Memorial Hospital in 1986. New in town, he rented a room from Lyla Montgomery while falling in love with Frannie Hughes. Lyla encouraged the young doctor to pursue Frannie, but she didn't return his feelings. After some time, Casey and Lyla fell in love, despite her being several years older.
Lyla and Casey married and she soon became pregnant with Katie. However, Casey was diagnosed with Guillain-Barre syndrome, a disorder that affected his nervous system.
In 1990, Casey's condition worsened. As he was about to be put on a respirator, and since his living will wasn't finalized, he asked Margo to let him die with dignity. She obliged and unplugged his life support, which led to his death.
Watch the videos below as Margo, pulls the plug and then confesses to her mother. Feel free to share your thoughts on the storyline in the comments.