Who will have won in the lore?
I think if it comes down to a future Elder Scrolls Game; they'll gloss over the details of the Civil War; and paticularly, who won. I think if we look at Skyrim in the future, it will not be an Imperial Provence, But it will not be ruled by Ulfric's line, but rather that decended from the old King's wife.
This satisfies both conditions; Ulfric is defeated and the old kings wife is proclaimed High Queen. However due to the death of the Emperor, the Empire disintegrates and Skyrim gains self rule
or
Ulfric declares his inderpendence and is named High King. Alas! he is assassinated by vile Thalmar agents, and the mootl votes a new High Queen in her place.
It could also be seen the other way, that Skyrim remains in the empire.
Ulfric is defeated and the old kings wife is proclaimed High Queen, and remains part of the Empire.
or
Ulfric declares his inderpendence and is named high King. Alas! he is assassinated by vile Thalmar agents, and the moot votes in a new High Queen, who decides that the best interest of Skyrim is to be part of the Empire
Ether way, future games can solve the matter by not going into much detail over the events and the victors of the Civil War. Or they can be cheap and proclaim Dragon Break (though I must admit, things don't turn out well for Ulfric, as much as I like his character)