I still think Barry is going to end up sacrificing himself for her and somehow getting sucked into the speedforce. It will be the most heroic and heartbreaking thing ever... then come Season 4, Iris will "sense" him and pull him out of the speedforce, and we'll see the "lightning rod" theory come to fruition.

Maybe Iris is the one who will suffer "A fate worse than death" - life without Barry (for a few months, anyway).