The True Blood actress played Maleficent on the ABC fantasy drama, but the character was apparently killed off in the first season finale.
"Who knows? On that show... there really are no boundaries as far as who comes back or not," Bauer van Straten told The Huffington Post.
A magical purple mist consumed the town of Storybrooke in the finale, with unknown consequences for the show's characters.
"I think that when that mist rolled in, anything can happen, right?" the actress said. "That's what I'm telling myself. When a purple mists happens, I think you're good."
Once Upon a Time producer Jane Espenson recently named The Little Mermaid's Ariel, Goldilocks and Aladdin's Princess Jasmine as three characters she'd like to see appear in the show's second season.
Series star Ginnifer Goodwin (Mary Margaret/Snow White) has also hinted that season two will be "a whole new show".
Once Upon a Time returns to Sundays at 8/7c this fall on ABC.
> Katee Sackhoff auditioned for Once Upon a Time lead role