There is no prospect of the Mad Hatter returning, because he doesn't have the magic hat, which has driven him mad. Our last scene is seeing him raving as he attempts to recreate one. For him, breaking the curse is a tragic ending. August is the character who's going to play some role in the conflict, not Jefferson.
All female characters of any note thus far already have Fairytaleland personas, except for Emma. Any fairy tale persona she acquires will center on swans, in some form, whether Ugly Duckling or Black. If they go the Swan Lake route, it could be that Emma Swan the ordinary human sheriff is her cursed form and the Fairytaleland uncursed form would be a fairy tale princess, no more but no less, born to Charming and Snow White. And the prince who loves her may lose her to the real world forever if he falls for the deceits of the Black Swan. If they go the Ugly Duckling route, she turns out not to be an ordinary human aka duck, but magic, a true swan.
Breaking the curse possibly will involve someone who truly loves Regina kissing her, possibly Henry, as Regina in effect breaks the curse herself by finding a happy "ending" of her own; Gold kissing the real world equivalent of Belle, whatever her name is; Emma finding her true love (August?). Or it could just be the boring old kill the sorceress to end the curse.