Apologies for breaking the echo chamber, but history has proven that most conquerors and dominators have not lasted vitam aeternam. I think that Napoleon would have ended up being defeated, sooner or later, by the stock of enemies he had. He was not invincible, and time would have worn on him.
But how much longer would it have taken? Would Alexander still have joined the Allies, or would it have been up to the rest of Europe, which had already sustained very severe losses, to continue fighting Napoleon?