Why does Naegi always appear in the closing credits along with the dead characters?
I was wondering this myself. I think there's a theory that Naegi is actually dead and this is his purgatory. We never find out what the most despair inducing event in history is because Naegi died before he could find out. He's the one who has a pretty generic high school ability. Hopes peak academy could actually be the test whether he makes it to heaven or hell in the afterlife. When they all leave we just see a shining light but no sense of the outside world. 

If you think about it, the school is perfectly looked after and the fridges are all restocked daily. But who could do that? If instead we picture it as a purgatory scenario it just sets the stage for Naegi to show he can overcome despair.

I think he shows up in the ending credits along the dead characters to show that he's actually dead and when they all appear at the end it means they were all dead. But they made it to the afterlife.