I can see people leaving Starfleet, turning their back against the crew or even turning bad, but I can't see any of them dying.
Eh, they could kill off Spock Prime (And leave him dead). It would bring tear-jerker Drama, he wouldn't be a character that would hurt them by removing him from the canvas, and it would enable Leonard Nimoy to retire again, this time going out with a Death Scene for Spock that sticks.
Now, I don't necessarily have a desire to see Spock Prime killed off, but, it would be the biggest bang for the buck, without hurting the canvas of characters available to use for future movies
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?