Fling Into Darkness and redirection

One of your Heroes deals 1 Target 3 Melee Damage.
If that Target now has 4 or fewer HP and Writhe is active, destroy that Target.

There are many circumstances in which the damage from the first sentence can end up redirected.  In the second sentence, does "that Target" refer to the original Target chosen by the player, or the Target that finally ended up taking the damage?

It's the target who takes the damage.