If you put it this way... in the game if you're in the middle of doing the civil war, and you call for a dragon to assist you in battle, then the dragon will stay and fight until the every one last of your enemy (the red dot on your screen) goes away. So yeah they will stick around until the enemies are dead before they fly off to the distance.The only good dragons we see here are Paarthurnax and Odahviing. Durnehviir is also a good dragon,, however lets hypothetically say that he wanted to become the next Alduin... He's going to have a difficult time getting out of the Soul Carin, which he is stuck there for eternity after being tricked by the Ideal keepers. The only way he can temporary get out is if the dragonborn calls for his name in a form of a shout.
Of course the Dragonborn can easily die under the game settings. That's why in the game it's best to become friends with the F5 key

I never said that he was immortal.
The fact is after Bethesda is completely finish with Skyrim by releasing the finial expansion, where you then take the fight against the the Thalmor, The Aldmeri Dominion is going to lose the war no matter which team you're on.
Dude you realize that this is a game, right? I don't care how big the Dominion is.. Their going to lose no matter what in the next great war. As far as the Stormcloaks being racists... well my friend that is your opinion. Not once have I seen a Stormcloak soldier trashing another race. Perhaps you did? If so please send me a video clip so I can see it for myself.
The only way to find out for sure is if we wait for the final expansion then we will see, eh?