Having read the convention debate, I doubt that mightily. It was pretty much a done deal. You might be right on the matter of the structural primacy given to international law in the Constitution, but from what I've been able to surmise, that was one of the key elements being demanded by our creditors.
Had Henry accepted George Washington's appointment as the first Chief Justice of the United States perhaps he could have had some influence in shaping the Judicial Power.
At that point, he probably didn't want to legitimize the process (a hard call at the time). I agree with you that the centrality of his thesis deserved more play in the process. He was not thrilled with the Enlightenment ubiquity of pagan inspired deism (something akin to heresy here on FR). I'm just finishing up Peter Gay's first volume on that topic and will have more to say on it when the second is done.
Some people don't respond when history calls. Henry was one of them.
I think that a bit harsh, but it certainly so appears in hindsight.
He would have been present for the formation of the Virginia/Randolph Plan. Could he have, from the beginning influenced what generally emerged as our Constitution four months later?
On June 9th delegate Paterson of New Jersey convinced the Convention to step back from the Virginia Plan in order for opponents to devise a more federal arrangement that improved the Articles of Confederation. There is no doubt that Henry would have immersed himself in this committee and its product, the Paterson Plan.
On 15-16 June the Paterson Plan was debated.
Madison shredded the Paterson Plan on the 19th. Had the best orator and debater in modern history, Patrick Henry been present, maybe the vote to accept the Virginia Plan as the basis for discussion by 7-3 would have been closer. In any event, Henry was no shrinking violet and would have been a prominent speaker along with Madison, Morris and Wilson.
I also suspect John Lansing and Robert Yates of New York would have remained to influence events if another large state delegate like Henry had likewise remained to oppose key elements of the Constitution.
Fast forward to June 1788 and Henry almost kept Virginia out of the Union. Had he attended the Constitutional Convention he would have undoubtedly affected the final product. If it met with his disapproval, he would have been as well equipped as Madison to debate the finer points. As it was, he was not, and federalists carried the day.