Well, if the terrorists get there first, they can use the base defenses against James and co. Might provide an opportunity for some of Starfall's characters to sacrifice themselves. (A note about that below) In addition, they'd be able to torture Shelton for more information (which I'm fine with, as long as they don't kill him)
If James and co. reach first, they'll have the base defenses on their side, and some terrorists will have the opportunity to escape and get back to the hangar with the bridge. Personally, the former option seems to provide more drama, since our characters have been on the defense for most of the story.
Two other things, while I'm here:
While Starfall asked us to kill all his characters, I think Neku should be spared, especially since his relationship with Snow has been built up for the entire RP. Alternately, that could give him the incentive to sacrifice himself, if Snow were in serious danger.
Also, a question about what's going on with everybody captured by the shadow creatures. I don't think anyone has any plans for that. We could have Kerzach and the captured characters win the shadow creatures over to our side. Then, now that we have an adequate fighting force, we can attack the hangar, and fight the terrorists to stop them from using the bridge, leading to the climax of the entire RP.
Actually, it kind of makes sense that they'd side with us; they are fellow Pelvanida personnel, and their commanders had just ditched them for the terrorists.