Duncan MacLeod wrote:
It's not his universe at that point, so it's not up to him.
This seems to be a moot point to me.
Spock has acted to preserve worlds with which he had far less connection than an alternate universe Vulcan.
And in any case it would still be genocide.
So, after the movie ends, he'll do his best to time travel and save Vulcan. (Does he know
how to time travel in this universe? Star Trek
folks have learned how to time travel before and then acted like they forgot.)
Or maybe he decides he can do more good alerting Starfleet to the Doomsday Machine which even at that very moment, is munching up planets and probably killing a lot more people than died on Vulcan, and helping them to extrapolate its path based on where he remembers it when the Enterprise
encountered it, so that they can destroy it before it can gobble up more worlds. Given the similarity of this universe to Spock's original one, and the lifetime of knowledge he has, there are any number of ways he could save billions of lives, and maybe futzing around with time travel isn't the best use of his time.