Karona's Zealot — ruling 1

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.

Karona's Zealot — ruling 2

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.

Karona's Zealot : règles, fonctionnement et interactions (MTG)

Karona's Zealot is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Morph (You may cast this card face down as a 2/2 creature for . Turn it face up any time for its morph cost.) When this creature is turned face up, all damage that would be dealt to it this turn is dealt to target creature instead.

How it works : Karona's Zealot

Original English text — Wizards of the Coast / Scryfall

#1March 16, 2018· Wizards of the Coast
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.
No other card is named in this ruling.
#2March 16, 2018· Wizards of the Coast
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.
No other card is named in this ruling.