Andy wasn't really a minor character? How many of Kira's enemies besides the gundam pilots survived?. Plus it was andy's supposed death that started his path in the no killing direction. Andy is far from a minor character, he is right up with Mwu.
We can say whatever the fuck we want as well. Like Mwu is alive. We have just as much evidence and right to say he is alive if not more. Unless we see a body there is no proof to say he is dead. We're all just making speculations on the evidence at hand. So aslong as there is evidence supporting Mwu being alive deal with it. And when we find out the truth in the end deal with the outcome like everyone else. The shows creators can do whatever the hell they want. They have left plenty of spots in the story to do either.