I'll start it.
Disclaimer: This is a non-canon discussion basing off non-canon assumptions for fun. "Lore-Master Police, Blademasters etc... can buzz off and let us have our fun"
Starting this topic with the most unreliable factor: Dragonborn.
(Since this is the first post of the topic, I'l not use too much opinionated assumptions)
If the Dragonborn comes into the picture. No matter which side he joins, the chances of winning against the other side of the Civil War becomes 100% whether it includes cut content or not and the chances of winning against the Aldmeri Dominion is also quite high too since Dragons are like demi-gods and cannot be killed by anyone except a Dragonborn.
Without the Dragonborn, I don't even think the Civil War will reach a conclusion anytime soon. It is pure bad luck but this kind of sh*t happens all the time. So yeah. Civil War don't reach conclusion, the Empire in overall continues to weaken.
As for what happens to Stormcloaks, most people are concerned with what will happen if they win. Those siding Empire says the Stormcloaks don't stand a chance against the Aldmeri Dominion if they become independent.
The truth is there's only 1 difference with Stormcloak victory over Empire's.
Stormcloaks will likely be trying to recover when the Aldmeri Dominion hits the Empire after the Civil war ends.
No matter what is the result of the Civil War, Cyrodiil is going to get hit. Indirectly, saying the Stormcloaks cannot win at all is indirectly saying the Aldmeri Dominion are going to obliterate the Empire's forces and the Stormcloaks can't take the Cyrodiilic Cities from the Aldmeri forces.
Why Cyrodiil will get hit first? It is far too close to the Aldmeri Provinces. Long travel journey also means longer expeditures in transportation and stretching their supply lines way too thin just to invade Skyrim. That doesn't make sense at all. They might as well hit Cyrodiil. If they can't tak Bravil, they can at least retreat back to Elsweyr and Valenwood - Friendly territories.
So yeah: Cyrodiil is going to get hit first no matter what. Since Hammerfell is not Empire lands, they are not likely to get hit. If anything the Thalmor might put on a poker face and tries to be remedy the relationship to cold or something with the Redguard so they don't have to face 2 fronts.