Sure in some kind of multiverse theory kind of way, there exist an infinite number of universe which always simultaneously happens. But bottom line is what happenned in the past Trek series have now minor impact to what's happening now.
It depends what you mean by "now." In 2009, just like in 1969, 1979, 1989 and 1999, the writers are creating new episodes that continue the "Star Trek" story forward logically from all episodes that came before it.
If you mean "now" as in Stardate 2258.42 in the latest movie, then all of Spock's and Nero's experiences in the previous timeline are still having a major impact on events. In fact, everything that took place in this movie was a direct result of what Nero and Spock experienced in the original timeline.
Thus the writers can creatively do what they want. Wiping out the Vulcans or maybe the Klingons or on the contrary making the Klingons the most powerful species in the galaxy.
But that's been true in
every past movie and episode as well. The writers could decide at any time to blow up Romulus, blow up Vulcan, blow up the Klingon moon Praxis, have the Borg go back in time and assimilate Earth -- and in fact they have done all those things.
This movie is no different from other time travel stories that alter events that turned out different in the original timeline.
When Admiral Janeway changed history, and got the Voyager home 20 years earlier, and we saw this alternate timeline in "Star Trek: Nemesis," that is no different than what the writers did in this movie. The last two movies both took place in alternate timelines that are different from the previous movie's timeline.
It may be a good thing but they have in all practical manner put the reset button on all past trek catalog. No multiverse theory will change that.
No theory has to change anything. As we saw, Spock could follow Nero back through the black hole at a later time, and end up in this new timeline.
So, as long as the black hole continues to exist, there is always the possibility that Picard or Riker or Worf or anyone else could follow Spock back and interact in this new timeline, or they could just stay in the 24th Century and continue with their lives without Spock and Nero.
There's nothing to stop CBS, which owns the TV rights, from creating a "Star Trek: Titan" series featuring Captain Riker in the Post-Romulan era of the Prime timeline.
It would be like the "Terminator" TV series, which runs independent of, but still connected to, the "Terminator" movies, just in an alternate timeline.
The point is that the writers of any particular movie or episode will do whatever they want. Maybe when these producers run their course, the next group will be DS9 fans, and continue the series in that timeline, with "Star Trek XVII: The Wrath of the Founders." No doors have been closed. There are always possibilities.
I think you, like a lot of people, find it acceptable for good people to do good things using time travel (e.g., saving the whales, getting the
Voyager home earlier, preventing Soran from blowing up the sun), but when bad people do bad things using time travel (e.g., blowing up Vulcan, trying to assimilate Earth, etc.), only then do you start complaining about the timeline being changed and the whole series being ruined.
When Picard prevented a planet from blowing up in "Star Trek Generations," creating an alternate timeline, how is that different from Nero destroying a planet in a new timeline? In time travel logic, it is NOT different, except that you consider one a "good guy" changing history for a "good" reason, and the other is a "bad guy" changing history for a "bad" reason.
But mechanically and logically, this movie is not doing anything new or different. It is simply the 736th episode in the canon, and its storyline continues forward logically from all the episodes that came before it. Like all episodes before it, the writers are free to tell whatever story they want to tell, and that will be true in the next movie as well.
