From the Fall 2000 issue of Sacred Music: "The Question of the Choral Sanctus: A Canon Lawyer's Opinion." I would certainly say that this settles the issue, which isn't to say that this one article will put an end to the claim that that the Sanctus must always be sung by everyone.
To me the most obvious point is the following: if the choral Sanctus were prohibited, a major part of the Mass Ordinary that has inspired composers for 500 years would be shredded and tossed into the dust bin of history (for liturgical purposes in any case). With the set of Ordinary settings broken up in this way, these compositions would be destroyed--an act not different from taking a wrecking ball to every Cathedral in Europe or smashing every stained-glass window, an act even more egregious since the Church says her musical treasures are of greater value than any other art. It would be a form of iconoclasm that is unprecedented. Is one poorly worded line in the GIRM capable of that level of destruction? Maybe but there is no evidence that this was the intent, especially given the example provided by the Popes, who celebrate Masses where the choral Sanctus is used.
So while this canon lawyer's opinion is valuable for fleshing out the legal details, a good sense of the faith is enough to shore up the case.