Actually, it really wasn't such a big deal for the French. By the time Trafalgar had occurred, Napoleon's focus had already shifted from the Britain to central Europe, and the Grande Armee had already evacuated its positions along the English channel and had wheeled around and marched towards into Germany and Austria. In other words even if the French had gained control of the channel there would be no troops available to cross.
There is also no real likelihood of the French actually gaining control of the channel at a later date. The disparity in fighting efficiency between the English and the allied fleet is such Trafalgar merely put a period at the end of a sentence that is drawing naturally to a close by itself. In a few words, Trafalgar had no immediate strategic impact and almost no historic impact. The French knew it, and they at the same time had far bigger fish to fry
In 2 month, Napoleon and Grande Armee would reach Austerlitz, and there against 2 to 1 odds would utterly crush a combined Russo-Austrian army to cement French hegemony over central Europe. The central European campaign, which was going on at the same time as Trafalgar, was strategically a far greater and more decisive victory for France than even Trafalgar was for UK. For the French, Trafalgar was just a setback on a front which had itself receeded into secondary significance. Trafalgar changed nothing for the French.
When Napoleon learned of the French defeat at Trafalgar, he was not much effected. Ships come and ships go, French power continues to increase. When William Pitt, the British prime minister, learned of the Russo-Austrian defeat at Austerlitz 2 month later, he ordered that all maps of Europe in the foreign office rolled up and put into storage, and died shortly after out of despair. This should tell you something about the relative significance of Trafalgar and Austerlitz.
If one must find a English strategic naval victory to rival Napoleon's Austerlitz, then one must look to the battle of Nile. Had Trafalgar not occurred, odds are today's world would still be much as it is. Had Nelson not won the battle of Nile, then Napoleon would have toppled the Ottoman empire, marched into India. A contigous French land empire rivaling the size of the Mongol Empire, stretching from the English Channel to the bay of Bangal would probably result, and 1.3 billion people in India would trace their heritage to French colonial influence rather then those of the British, and 19th century would have seen French supremacy rather then English.