So, this is awkward. After six seasons, Jennifer Morrison will leave Once Upon A Time despite being invited to continue as a series regular. She's "decided that creatively and personally, it is time for me to move on," which, OK, fair. So how will Emma Swan get written out of the show if it continues? After all, the blonde actor plays the lead role, that of Snow White and Prince Charming's daughter, who started the series dragged into a quest to break a curse and restore her all the fairy tale characters' memories. You know, if she believed in curses and fairy tale characters, which, at the time, she did not.
If the show is renewed for a seventh season (which, minus the lead character, remains to be seen), then the team behind your fairy tale favorite are going to have a serious challenge on their hands: a write around deft enough to account for Swan's absence. Arguably, their options would be limited by what Morrison has already outlined, that she is willing to "to appear in one episode." Given this limit, their explanation for the former bail bond agent's departure will have to be relatively abrupt. Let's explore the possibilities.
One possibility could be giving her character memory loss. We've seen this storyline before in that bizarre Season 2 plot in which Belle was pushed over the town line and thus lost her memories of being, you know, the Beauty from Beauty and the Beast. After spending some time as an amnesiac in a hospital bed, Regina then gave her fake memories of being a heavy drinking sexpot named Lacey just to mess with Mr. Gold aka Rumplestiltskin aka Belle’s love interest). Lacey didn't last long before Belle abruptly got her memories back, but Emma could be given altered memories that they can’t undo and the best thing to do for her is to let her go have a normal life.
This would work because it would only demand one episode of exploring this new development, with the other characters trying to coax her back to a knowledge of who she is but then ultimately giving up. Sure, it isn't the most elegant farewell to a lead a series will have ever seen, but it's consistent with what we know of the world the show has built.
Alternatively, one goodbye that might make a sad sort of sense would be to have Emma leave town via force. Again, this would be consistent with what we've seen before. Midway through Season 3, due to a series of complicated magical events that would cause Storybrooke to disappear from existence and every fairy tale character therein to be transported back to the Enchanted Forest, Emma left town with Henry (as they were the only two non-fairy tale characters there). As such, the showrunners could do something similar for the Season 6 finale, in which Emma and Henry drive off to build a new life elsewhere to avoid something only unavoidable to fairy tale characters. (Of course, this might complicate her marriage to Captain Hook, but Morrison leaving is going to complicate that as well.)
It remains to be seen how they'll write out Emma, but here's hoping they make that one last episode really count.