The Scot's Magazine mentions a Russian General Sacken who apparently would be this gentleman. https://en.wikipedia.org/wiki/Fabian_Gottlieb_von_Osten-Sacken
Casual sources indicate that during the 100 days war that he served under de Tolly. No mention of having diner with Berthier.
No obvious memoirs; might be interesting.
Interesting dramatic detail about son holding on to his feet and almost being pulled out of the window.
That the attending doctor's assumption is called into question is important and works to negate his opinion on cause of death.
Honestly, had to look up defenestration and saw this usage "death by defenestration has a venerable history"