BEWARE - MOVIE SPOILERS IN THIS POST
Forty years of Star Trek canon has been thrown away!
No it's not. What we have to ask here is: does the universe in which all the other series were set in still "exist"? Spock and Nero are thrown back in time from 2387 to 2258 where Nero destroys the USS Kelvin, killing James T. Kirk's father and altering his life, and then destroys the planet Vulcan making a major change to the United Federation of Planets.
Spock specifically says in the movie that Nero's changes to the timeline create an "alternate universe" which in Treknological terms (what the unkindly might call technobabble) is "a separate and self-contained universe existing as a consequence of different choices and outcomes than those that have led to our own [or prime] universe." The concept is a bit of a stple in sci fi, in one episode, "Parallels", there are Enterprises from 285,000 universes altogether at one point!
The definitive canon answer comes from the writer, Bob Orci, in a conversation he had with Anthony Pasquale in December last year on Trekmovie.com ...
Anthony: OK so let's call the timeline Nero left, as `the prime timeline', soOK, so where does that leave the destruction of Romulus?
that means that the USS Kelvin, as designed and seen in the trailer, that is
also in the prime timeline?
Anthony: So what happens with the destruction of the Kelvin is the creation of
an alternative timeline, but what happens to the prime timeline after Nero
leaves it? Does it continue or does it wink out of existence once he goes back
and creates this new timeline.
Bob: It continues. According to the most successful, most tested scientific
theory ever, quantum mechanics, it continues.
Anthony: So everyone in the prime timeline, like Picard and Riker, are still off
doing there thing, it is just that Nero is gone.
Bob: Yes, and you will notice that whenever the movie comes out, that whatever
DVDs you have purchased, will continue to exist.
That's canon in the "Prime Universe", it happens in 2387 and it is proving to be an a major stumbling block for some fans. There is a whole section of Trek fandom that specifically focuses on Romulus, with their own fanon lore and language resources, that is understandably upset about the idea that the central planet of the Star Empire has been summarily blown away from Star Trek canon!
The future must seem very uncertain for them however this could be seen as an opportunity for a more exciting future for their chosen section of fandom. If we take the oft given advice that good storytelling needs conflict to excel then this could as literally re-invigorating the Romulan sub-plot. Was Remus destroyed as well? Will the Remans and other subject races use this as an opportunity to throw off the reins of the empire? If relations with the Federation have been improving since the events of Nemesis will the Empire turn to the UFP for help? Or will they see the destruction as a failure of the Vulcans as Nero did and drop back into their old xenophobic ways? The Romulans could be in a lot better situation than the Vulcans are in the new continuity because, as with the ancient Roman empire, there would be survived by colonies, planets and whole star systems that would consider themselves ethnically and culturally Romulan even though they might not have set foot on Romulus itself.
The other vexing problem that the destruction of Romulus will cause, is that some fan productions, most noticably some fan fiction series, are supposed to take place after 2387 and do not (of course) mention the destruction of the Romulan homeworld. I truly sympathise because I know that they not only represent an objective investment of time, skill and commitment but there can also be a very personal attachment between a fan fiction author and their book. I'm sure professional authors feel a similar connection with their work but they are primarily professionals, what they do will put food on their table and send their children to college. A fan fiction author is telling a story that is a part of them, their baby.
The truth of the matter is that no fan production will ever be canon even though the majority of writers and producers try their best to make their productions mesh with established canon, researching the technology, locations and cultures so that their own work rings true to other fans who might be reading.
Fan fiction authors caught in this situation still have a few options. They could add a disclaimer to their story to the effect that their work follows Trek canon up to 2387, a prospective reader could think of them as an alternate reality that branches off at that date. Alternatively, if a large enough number of authors agreed they could cooperate on a continuity that specifically saw the 2387 destruction of Romulus as an event that happened in an alternate universe, making their own "fanon universe". Examples of such Fanon cooperatives are USS Liberty, United Trek and many of the Virtual Seasons like Star Trek: Reborn. Or they could "retcon" their previous works to whatever extent they wanted or felt was necessary to bring it into line with canon.
I would encourage new works to include the 'Romulan event', personally I can see how it could open up a lot of plot possibilities but the idea of multiple alternate universes needs to be handled delicately - at what point does more freedom from canon become anarchy? Would we be in danger of having a Japanese style attitude towards canon where Anime characters and plotlines can change from one season to the next?