Not much to add here — I would like to know if Skyrim implements multiple endings.
There is no "ending" in Elder Scrolls games. There's the main quest line, but the game doesn't end: it just wraps up like any other quest chain.
That is, if you decide to finish the main quest line and
the NPCs related to that quest will react1 to the outcome.
If you don't, or even if you do, you'll just keep playing until you get bored. NPCs will continue to react differently depending on what you've done throughout the game, not just in the main quest line.
Note 1: Depending on your actions, there's a specific cutscene that may or may not trigger:
The Answer to your question is like stationed above, it will never end. Even the Dark brotherhood is set to have a never ending quest line, but it does have a main quest that can be finished. Which sadly is kind of short.
You have quest all over the place in this game, from going on quest that's related to Oblivion in origin an ones for Morrowind.
So it really just matters to have fun and play the game till you get bored, which seems to be hard to get bored of, LOL. Almost felt like quitting my job for the game!