About Vulcan...
We see both Earth and Vulcan getting attacked by the big mining laser. I think Nero heads to Vulcan first, destroys it, then moves on to Earth. Meanwhile, Old Spock sets the young crew on not just stopping Nero, but reverting the time line to what it originally was. I'm sensing sort of a "Year of Hell" or "All Good Things..." type sacrifice at the end, and when they are dead, they also accomplish whatever it may be to return things to the time line that we all are familiar with.