Pamela was severely burned after driving a car into an oil tanker, which then exploded into flames, in the season 10 finale in 1987. During season 11, Pam disappeared after her half-sister Katherine Wentworth was seen around the hospital, with Pam seemingly leaving Bobby and Christopher due to her unwillingness to let them see her in such a physically disfigured fashion. While Victoria Principal never returned to "Dallas" again after the season 10 finale, Margaret Michaels, a Principal look-alike, played Pam in the opening episode of season 12. Having undergone plastic surgery which explained the difference in her appearance, it was revealed that Pam was dying of a disease, though only she and her doctor knew about this. After this episode, Pam is never seen in "Dallas" again. Unable to reach a salary agreement and having a desire to start her own business, it was Principal's own decision not to return to "Dallas" again after the season 10 finale.