A cargo door or cabin door opening during take off and in flight is a very serious even in most aircraft.
When I trained on the Beech many moons ago, it was made
very clear to me that the cargo door on the 1900D is structurally critical. If the door comes open, it will soon separate - destroying the empennage in the process. To paraphrase: 'If the red light comes on, land NOW, because you're already on borrowed time.'
That's how I remember it, anyway. Would any other 1900D drivers care to expand on/refute that?