Louis Joseph, the seven year old son of Louis XVI, happened to die on June 4, 1789, right in the middle of the meeting of the Estates General; the king, naturally enough, was wracked with grief. It was in his absence that the Third Estate declared itself the "National Assembly"; and it was a still grieving Louis who tried to disperse them, leading to the Tennis Court Oath, and from there, and who gave a less than diplomatic speech trying to get the Estates General back on track, only to be defied by the emboldened delegates.
So supposing the prince had not died at such a delicate moment (surviving at least another few months)? How is the course of the French Revolution changed (or is it still a revolution)? And how is history affected from there?