I don’t think that there is any way that Jennifer filmed a scene for a future episode. The answer was no to is she coming back, so that is it. Also, they would then have to pay her for another episode and she said she was just contracted for the one. I think it is that and done.
Emma might just be happily off somewhere else and can’t get to where Henry is at. Or Henry wants to deal with it on his own. Or maybe Regina is our Regina and the other two are not. I think that no matter what happens to Emma, whether cursed or dead or in Storybrooke or another realm, people are always going to be asking because she was the main character and the show can’t really work without her.