certainly, napoleon's death is on the cards.The probability of Britain agreeing to peace with Napoleonic France is equal to the probability of Napoleonic France offering an Anglo-French peace which Britain can possibly accept: that is to say, zero. To say otherwise is to grossly misread Napoleon I's personality and actions, and the enormous mutual hatred between Napoleon I and the British. Napoleon I would demand British submission and keep fighting until either he achieved it or he believed he needed a pause in his wars; the British would fight on against Napoleon even if his troops were marching in London.
Post-Napoleonic France, on the other hand, is somewhat more possible. So, as seems to be the case so often, the easiest solution is "Kill off Napoleon in battle and have someone else, like a regency or the Marshals, take charge". If that isn't permitted by your intended scenario, you'll have to be… creative.
so, we would be having: 1. british navy crippled during battle and 2. napoleon dead.
we could also make the 1797 riots in Britain larger so much as to cripple the social system, maybe..
with these factors, could we possibly see how the oceans of the world will not be dominated by British flags?