Antonyms of downfall:
rise, advancement, development, evolution, growth, blossoming, flourishing, flowering, renewal, restoration, revitalization, heightening, accretion, accrual, addendum, addition, augmentation, boost, enhancement, gain, increase, increment, raise, supplement, ascent, upswing, advance, headway, progress, flower, heyday, prime, aggrandizement, exaltation, up, drizzle, mist, mizzle, scud, spit, sprinkle.
Examples of usage:
  1. The clay surface held water, and after each downfall the pools would be higher, and the contour of the little region altered.
    "Edge of the Jungle", William Beebe.
  2. There was a great pause, for none of us, when he did appear in sight, could shout over the downfall of so merciful a conqueror.
    "The Scottish Chiefs", Jane Porter.
  3. We could tell a number of such stories where we feel confident that a very large family on very small means is largely to blame for the downfall of the older daughters.
    "Commercialized Prostitution in New York City", George Jackson Kneeland.