I wonder how things would have worked out if it was he [Decker], not Kirk, who handled the V'ger situation.
Enterprise would have been destroyed. Decker wanted to raise shields approaching the cloud, but Kirk overruled because it might have been seen as a provocative move.
He later lets his emotions interfere with reason when Ilia is killed. When the mechanical Ilia appears, he gets all goo-goo eyed over her and has to be snapped out of it by McCoy.
So if Kirk and McCoy hadn't been there, the film would have ended without the true nature of V'Ger being discovered. Odds are Spock wouldn't have been there either.