Historically, in Star Trek, when the timeline is "broken", it gets "fixed". When Nero went back, he changed time. Now, if you subscribed to The Doctor's statement that there are fixed points in time that cannot be changed, then Nero's incursion would have happened in the Prime Verse... but this isn't Doctor Who. It's Star Trek. Star Trek makes things right, or else the Enterprise C wouldn't have been sent back to die. Needs of the many. The timeline is changed. Who knows what life is going to be like almost 200 years after Kirk and Spock? How do we know that the Narada didn't automatically jump-start the Borg? It was built with Borg technology, after all? So being faced with a future where humans, Klingons, Ferengi, Tholians, Vulcans, Romulans, Bajorans, they're all on the fringe, working together to fight a huge foe, sacrificing everything they are to restore a timeline where all of these races have fought together to keep the Dominion in the Gamma Quadrant and the Borg in the Delta Quadrant, where there is peace for our half of the galaxy... I think that's more than fixing something that's not broken... I think that's something we, as an audience, could get behind and root for, whether we know what the Prime timeline looks like or not, it's gotta be better than what we (could) have.