The actress' character Pamela Ewing was written out of the sex-and-scandal series in 1987 when viewers were told she had only months to live after fleeing the Texan dynasty.
But the storyline was left open-ended, and it's now emerged Principal - who is the only surviving member of the show's original cast not signed up for the relaunch later this year (12) - could be brought back to Dallas in an explosive plot.
Duffy, who played her onscreen husband Bobby Ewing, and Metcalfe, who stars in the reboot as the couple's adopted son Christopher, have both hinted the show's producers would be happy to bring Pamela Ewing back if Principal agrees.
In an appearance on U.K. morning show Lorraine on Wednesday, Duffy said, "Our producer has said that any actor who's still alive (and) who was on the show, the option is that that character could come back."
And Metcalfe tells British talk show Loose Women, "She hasn't (come back) - she hasn't as yet. But I think for the producers of the show, it's an open invitation."