I also express my doubt about that the Empire would just let Skyrim go after the war. Why the hell would they? They just fought a bloody war to keep them under Cyrodiil's boot, why just let them go now without a fight? Makes no sense.
Can't say I've seen that line anywhere.
As for SCs kicking the Thalmor out, yes it's a great thing that they would do that. But there are a whole lot of other places where they need to be kicked out too. And a united Empire is the most viable option to do that. Question here is if you care more about Skyrim or other parts of Tamriel. SCs do a lot of good for Skyrim, no denying that, but if we want to take the fight to the Thalmor itself, we need mankind to stand under one banner to do that. And as I have said, after the Thalmor is gone I won't care whether or not Skyrim remains in the Empire, or if the Empire itself remains. I want Valenwood and Alinor liberated ASAP and that's all I care about.