Maleficent was a dying candle. Her "light" (her power, her knowledge, her plans) flickered and swayed, this close to being blown out but never getting a step closer, never actually dying despite her enemies' best efforts.
Maleficent cast dark shadows over everything, darker than a Heartless' body or Riku's heart or the pathetic sniveling souls and minds of the Organization. She shaded everything, made enemies out of friends and laughed as they spilled poisoned blood and poisoned words.
Maleficent was dying dying dying all alone, with no Princess or ally or power to see her off into the final Abyss.