Another interesting thread. I would note that the term "advantage" has not been used in any of the responses. Keeping in mind the proper application of this principle, how does anyone defend calling a foul and penalty kick after the ball has already gone into the net? Also, it didn't jump out at me immediately that this was not a "goal scoring opportunity" (since there is the possibility that the ball will ricochet off the wall), but I think this analysis makes a certain amount of sense and would warrant keeping the redcard in your pocket. (Of course, even though it wasn't a goal scoring opportunity, this doesn't change the intent of the defensive player, who thought he was going to stop a goal by using his hands. Reminds me of the old question of whether a defendant can be found guilty of murder or attempted murder after sneaking up and shooting someone in the back of the head only to learn that the person had died of a heart attack hours earlier).
The player who attempts to handle the ball has simply tried to deny a goal-kick opportunity. (whether he knew it or not) The goal stands as the ball has been touched by a second player and thus, fufills the requirements of an IFK. No further action is necesary. Kick off. Keep it simple, dont go looking for trouble.