A star exploding is a pretty hard thing to stop, it occurs because the star runs out of fuel, Nothing anyone has done so far in this new timeline will stop that star from exploding, and Spock has very good reason not to reinvent red matter after it has destroyed his homeworld. The Romulans might try to invent the stuff, but they also have about a century before that star explodes and destroys their homeworld if they don't succeed, and many Romulans won't want to take the chance of being on Romulus when it explodes. Romulans are fairly long lived being related to vulcans, many are going to try and get off their home planet, and this will result in a mass migration of Romulans into space on an unpresidented scale, not only of Romulus but of any planet within 50 light years of that star about to go supernova, this may lead to a more aggressive Romulan Star Empire as it seeks to conquer new planets to accomodate its evacuating population.
I like the way you think!
It would be great if the next film is based on something that is a rational extension of such a significant and founding event. There is obvious potential for dramatic stories, intellectual and moral considerations and even the odd explosion or two (as befits a "two hour movie" I understand).
In a way it would be a shame if Nero had already destroyed the offending star. But it would have been nice if the movie had actually explained what it meant by things like "I prevented genocide!" as mentioned by Timo.
A natural disaster isn't genocide. If the implication is that Vulcans caused it somehow, then Nero's comment is probably referring to the destruction of Vulcan. In that case the is no longer a threat to Romulus but of course Nero is probably mistaken. Damn the writers strike!
Actually Spock probably failed to save Romulus and Nero was accusing him of neglecting it intentionally, and that is what send him on his course to get revenge on Vulcan. Spock probably sees it as his doing that destroyed Vulcan with Nero as the vehicle for that destruction, but he accepts no blame for the destruction of Romulus. And if the Romulans want him to make some more red matter, he would probably refuse if he could, or he'll say since the Vulcan Science Academy no longer exists, he'll apologize and say sorry it was a team effort and since a renegade Romulan from the future destroyed his planet, there is nothing he can do.