Yet another interesting idea, Gamma. I wish they had tackled that question at one point, in an episode. It would've been cool to see something like that happen at least once. For example, in an instance where David is hulking out, but realizes his hulking out at that particular moment will mean the Hulk (and he) will get killed. It could be a case where David is surrounded by a large group of fully armed military men with no way to escape (pointing their machine guns at him), and he knows that The Hulk will certainly get killed as he charges at them. David would start to Hulk-out, and upon reaching Demi-Hulk stage, use every ounce of self-control he possesses, to force himself to revert back into David. The military men would witness this and be in shock, but would not fire.