Quote mamarock: Pam left Dallas when she become ill and never contacted anyone. Nobody knows!
Actually Bobby tracked her down after she had plastic surgery to repair some of the damage from the crash. She told him she was happy where she was, but she actually had a terminal illness and didn't want Bobby to know. She didn't want Bobby and Christopher to watch her suffer before she died. That was the last time anyone saw Pam. They had a movie a few years ago that implied she was dead? Don't know if they will rewrite history or not.