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...
Events in the NuTrek universe already aren't
carbon copies of the "Prime" universe, and this is before
Nero and Spock RIP THROUGH space-time. Then you have countless deaths and changes in events as a result of their intrusion which would not have occurred, a planet which is obliterated, never mind 4 instances of RIPS and HOLES in the space-time continuum. You can certainly believe events from one reality may
copy in another, as they have been proven to do so in many regards. But you can't conclusively claim events from the "Prime" universe will
repeat in this one with any amount of certainty. See Parallels
for reference - hell, see ANY alternate universe episode for reference.
Centurion: "...power is danger."
Romulan Commander: "Danger and I are old companions." - TOS episode Balance of Terror
"Living in your dreams is like living in exile." - Calyx, A Stitch in Time
"Shame on you, Barack Obama!" - Hillary Clinton
"It's the economy, stupid." - Bill Clinton