To be honest, just based on the dialog of the scene on the bridge where they presume Nero is from the future, what happened is open to interpretation. Whether they're now a branch of the prime timeline or they're essentially "recording over" the prime line, in either case it's an alternate timeline, their destinies have been changed, and no one can predict the future. There's not enough information from the discussion to conclude whether or not something new has been created or if an existing timeline has been changed.
However, if the "TOS timeline" had been changed, the question within Trek storytelling would be: how is it corrected? I don't think it can be, and that proves it's a new timeline, not a perverting of the prime one. Consider, if someone did try to go back in time to stop Nero and the Narada, that would still change time, not "correct" anything, because Nero and the Narada never existed at all in the TOS timeline.
To my tortured reasoning, that's the best on-screen evidence that a new universe was created and the old one still exists. There is nothing to correct in the new universe. The moment Nero appears, a new timeline is created whether things happen as they did in the movie or otherwise. The only way to prevent the new timeline is to travel to the future of the prime universe and prevent Nero (and Spock) from going into the black hole in the first place. Of course, that new universe doesn't exist without Nero's appearance. So -- .
And with that, I'm outta ammunition on this.
However, if the "TOS timeline" had been changed, the question within Trek storytelling would be: how is it corrected? I don't think it can be, and that proves it's a new timeline, not a perverting of the prime one. Consider, if someone did try to go back in time to stop Nero and the Narada, that would still change time, not "correct" anything, because Nero and the Narada never existed at all in the TOS timeline.
To my tortured reasoning, that's the best on-screen evidence that a new universe was created and the old one still exists. There is nothing to correct in the new universe. The moment Nero appears, a new timeline is created whether things happen as they did in the movie or otherwise. The only way to prevent the new timeline is to travel to the future of the prime universe and prevent Nero (and Spock) from going into the black hole in the first place. Of course, that new universe doesn't exist without Nero's appearance. So -- .
And with that, I'm outta ammunition on this.