What I thought was interesting in the What Happened to Frederick episode was how bothered Regina was by the fact that Kathryn was clearly beginning to think for herself and was separating from the “character” that had been created for her in Storybrooke. She was basically becoming her own person who wasn’t associated with David in anyway and therefore, was no longer a “character” in Storybrooke.
Although David has brief moments when he is tempted to step out of his character’s Storybrooke box and go after Mary Maragaret, he always finds a way to screw everything up and ruin the moment. With Kathryn, this is the first time we have seen a character stray from they way their FTL character should end up, and/or stray from the way Regina would want their Storybrooke character to end up. To have her FTL happy ending, Kathryn should have found Frederick’s equivalent in Storybrooke and wanted to be with him but she was too busy to even notice him when she bumped into him at the school. Instead she decided to be her own person and move to Boston to go to law school and start over with a fresh new life.
It seems like either Regina had to do away with Kathryn because she had broken out of her Storybrooke life or, once a character deviates from both their Storybrooke character and their FTL character, something goes horribly wrong with their existance. I never really thought about the fact that the characters could have the ability to make their own choices in Storybrooke and choose to NOT be with their FTL significant others. Since they ARE truly Fairy Tale characters, making decisions that go totally against both their Fairy Tale story and the Curse could cause them to be in a kind of limbo. Because then who would they really be? Take Kathryn for example. If she isn’t Abigail anymore and she isn’t David’s wife in Storybrooke (whose sole purpose is to keep him away from Mary Margaret), then who is she??? I don’t think she can leave Storybrooke, but assuming she could, – who would she be, what would her background be? She has existed in the vacuum of Storybrooke for years until Emma arrived – so would she even be able to exist outside of Storybrooke???
So this makes me wonder if we will ever find out what happened to Kathryn. Maybe she really just disappeared because she made a decision that caused her Storybrooke “character” to no longer exist.