I hosted a Napoleonics game for the guys this past weekend that was another one of my hypothetical 'what-if' scenarios - as JohnB was kind enough to bring down his beautiful Russian collection from Saskatoon, this game was set in Poland around Christmas 1806.
First, the 'true-to-history' bit:
October 1806 had seen the French crush the Prussian army at the twin battles of Jena-Auerstaedt and by December Napoleon his Grande Armee was encamped in Poland, preparing to bring the Russians at bay in the upcoming spring campaign.
Wanting to catch the French unprepared while they were scattered in their cantonments, the Russians decided to initiate a surprise winter offensive. Nonetheless, by pure coincidence, at that same time Marshal Ney unilaterally decided to move his corps forward into a better foraging area. So the two forces began to move very near to one another, close to the Baltic coast.
In London, with the defeat of the Prussians and the subsequent advance of the French army into the Baltic region, the British were becoming very concerned that Denmark, with its significant navy, was at risk of being annexed by France or worse, would be convinced into a French alliance. Accordingly, discussions had been going on between Britain and Denmark with the British 'offering' to quarantine the Danish navy until the end of hostilities with Napoleon. Not surprisingly the Danes were not interested.
Now, my hypothetical premise (i.e. 'made-up tosh'):