(My problem, however, is getting them to accept a shorter ending.)
That's true with me as well. The players don't know the ending, of course, until they run it. I don't like to give them out-of-game context like, "We'll be finishing up this storyline in a game session or two."
Sometimes, when the game is over, the players are shocked. Sure, they just saved the princess, defeated the rotten empire, morned their dead, and have no other objectives that haven't yet been cross off their list--but, it's still a shock when they find out the game is over.
I get accused of being a "quitter" in my group sometimes, mistakenly, because of this. It's become a bit of a joke.
"You're a quitter!"
"I am not. The story was over!"
The most famous of these types of encounters with my players happened in a D6 Star Wars campaign. We finally faced Vader--my goal all along. But, it took us so long to get there. We played the characters from the time the Death Star was destroyed, to the PCs becoming involved in the Rebellion, all the way to the PCs meeting and confronting Vader (who, basically, kicked their asses). But, still, the story came to a close. The game was over.
"You're a quitter!"
"Dude! We played the campaign for SEVEN YEARS!! We faced VADER!! The story is over now."