It would be great if there were a certain reaction to the count/countess death. In oblivion it was just meh. Is anything like this planned for skyrim?

I think with radiant story they will probably substitute the death of the count with someone else and maybe even put in a temporary council.
I think people will knowledge it with radiant story and standing will maybe rise with the other counts, and fall with the count's former subjects.

if all but 1 of the counts/ countesses die, the civil war would end and that would probably take a bit out of the plot of the game