That's what they did, in a sense. They said that the decision below should be upheld (reinstated, whatever), if there was evidence of that nature. In order to provide for the entry of evidence, they had to reverse the decision below, where the indictment was quashed, because without a proceeding, there was no place for the judiciary to obtain evidence.
-- Mr. Miller's counsel didn't appear to argue the other side of the case, the weapon in question was a short barreled shotgun not an automatic weapon ... --
Yes, and the short barrel shotgun had widespread use by then, and similar had long been in use (blunderbuss) as military and defensive weapons. Bigtime use in trench warfare in WWI.
-- I believe that by the time the Supreme Court heard this case Mr. Miller had met an untimely death. --
He was a no show, and I think you are right, he was a no show because he was dead.
That said, the precedent is chronically misread and misapplied. Scalia did so in the Heller case; at first saying Miller's conviction was upheld! Ummm, Miller was NEVER convicted. The indictment against him was quashed.
It's really bizarre. These are presumably the nine sharpest jurists we can find, and if you listen to Scalia talk, he's unquestionably a very smart guy. So what the hell gives with this kind of stuff? I can see errors in reasoning, especially from progressives, but to misstate simple historical fact, particularly in a field in which one is supposedly at the top of the heap? What the hell?