I think they will find the cure and Rebecca will take it and turn human and find out that it turns your body to the natural human state you'd have been in had you never become immortal. So she turns into a thousand year old pile of bones or dust. Elena can take the cure and return to normal since she'd have only aged a year, Caroline could as well, the Mother, etc... but neither of the mains could since they were turned in the mid 1800s so it restores to the show to where it was when it began vampire wise.
And I'd be totally fine with that too. So long as Rebekah dies - then I only have to watch one whiny crying Original sibling and one annoying werewolf as I'm watching The Originals for the awesome Elijah.