Normally the pokemon using takedown will lose. In the game, if recoil damage kills a pokemon, & another pokemon then dies of poison, the poisoning will happen at end of turn so it technically was KO ed last so the trainer with the pokemon that was poisoned won.
This is what has happened out of my personal experience. hope it helps :)
EDIT- I just remembered something else; the recoil would damage the opponent right after the move was used. In some games, the end of turn damage is not calculated if the first fainted pokemon has fainted (ex if in a hailstorm & you beat the wild pokemon before the first turn is over, you won't be hit by hail). Normally, a pokemon (unless seriously damaged) won't die of recoil, but that is an interesting situation