With a new Red Woman being introduced on the show this season, and the writers revealing Melisandre's true age and form for the first time in the Season 6 premiere, tuned-in fans would hope for some priestess payoff this season. For Melisandre, "rebirth" could mean death -- who knows why the Lord of Light wound up imbuing her with his magic, or if her mortal presence is even a true form.
A Game of Thrones death is always grisly and momentary, a morose reminder that life can be snatched away in an instant. If Melisandre's time is up, a transcendent death, one that releases her into the Light, could fit the season's theme. Or maybe it's as simple as the reneweal of her faith in the wake of Jon Snow's resurrection.