His assasssination ended the Non-Aligned nations, which Britain attacked Denmark-Norway to prevent them from joining and to get their navy, so it didn't fall into the hands of the French.
that might just be what pushes Russia over the edge to allying with Napoleon, too. Feeling an attack on Denmark-Norway deserved such a response.
In this scenario, with France a year away or so from getting the Treaty of Amiens and seeming to have won, it's more likely France will force the British to make a treaty even sooner, maybe 6 months or so earlier? France will still try to go to war again, knowing Napoleon, but this time it'll be Britain, Prussia, and Austria agaisnt him in the Third Coalition.
With Russia now on the French side, i wonder if they try to convince the Ottomans to attack RussA to draw off some of the French allies' strength.
Then again, you still have the huge British navy, which means they likely still win Trafalgar. So, maybe not a hgue different a decade downt he road, as Napoleon might still feel like attacking russia.