If the target creature leaves the battlefield or stops being a creature before damage would be dealt, that damage is not redirected. For example, if you choose a 1/1 creature, then Karona's Zealot would be dealt 3 damage, all 3 is dealt instead to the 1/1 creature, which then dies. If Karona's Zealot would be dealt 3 damage again later in the turn, the 1/1 creature is no longer on the battlefield, so the damage is not redirected.

If multiple replacement effects would modify how damage would be dealt, the player being dealt damage (or the controller of the permanent being dealt damage) chooses the order in which to apply those effects.