Patrick Henry viewed the American Revolution as a war against an overweening central authority, not an effort to establish a new nation. He turned down an invitation to participate at the Convention because he disagreed with the mission; he later led the fight against ratification. What if he had decided to go to Philadelphia? He was the foremost orator of his age; would that have made a difference?
If he had broken his promise to keep the proceedings secret, maybe. Otherwise, no. The Founding Fathers were hardheaded politicians; it is unlikely that they would have been swayed by speeches, however eloquent.