In a double battle, both opponents are targeted, but only the one that knocks the user out is affected. If the partner Pokémon causes the Pokémon using Destiny Bond to faint, the partner Pokémon will not be affected.
A Pokémon defeated by this move will now faint after the Pokémon that used Destiny Bond.
In a triple battle, Destiny Bond affects all of the opponent's Pokémon. If a non-adjacent Pokémon used a move that damages non-adjacent Pokémon (e.g. Aerial Ace, Air Slash) and knocks out the user of Destiny Bond, that Pokémon will faint as well.
so no the pokemon that takes out the foe is the one that faints because destiny bond affects your team not one individual pokemon.