If redirected, the damage does not take this effect with it. Disintegrate d creatures do not go to the graveyard at all before leaving the game. They do not trigger abilities which happen due to a creature going to the graveyard. Note - Also see X Costs, Rule K.27. Then destroy it cheaply with the other card.
Damage is doubled, or damage is done to two targets.
While the latter can damage multiple targets, the former has the nice ability of negating regeneration as well as making sure that you will never see that creature again.