Board Thread:Show-Related Questions and Answers/@comment-5344051-20160229080952/@comment-25733960-20160925233559

But it was said several times that there was no way to escape the Dark Curse

Maleficent said it when the Fillers of Darkness asked for help in 4x13 (I think)

Even more, if they could escape the Dark Curse just like that, Maleficent didn't need Snow/Charming's help in 4B and Cora's shield was pointless. They only needed to teleport themselves somewhere else, out of the curse radius.