If the dark brotherhood quest didnt happen,

[zuko514]

the wedding of victoria Vici went on without a hitch and the empiror was still alive, do you think it will make a difference in the civil war?

 

[Seanu Reaves]

The wedding? Eh probably not. But that dude would probably have nice sexy times before his merchant wife takes over every aspect of his life.

As for the Emperor, maybe? I mean Tulius does acknowledge the death of the Emperor if you join the imperials after killing him. But he still keeps fighting.

 

[DrunkenMage]

It wouldn't affect the Civil War right away, but it would cause a political shift. Leading to a peaceful resolution or treaty possibly. Never underestimate the power of a royal marriage in Tamriel.