SPOILERS! After Another.
This post has spoilers in it, please do not read if you haven't seen the show, and dotn liek spoilers.
I wonder, what happens after "Another"? I mean, Mei can see who the Dead One is, right? I understand why she didn't reveal it earlier, even if it was in actuality just a plot contrivance. She didn't know that killing The Dead One would end the calamity. In fact, she didn't know you could kill The Dead One. For all she knew, if you shot or stabbed or otherwise did something that'd kill a normal Human on The Dead One, it'd have no real effect. Only after hearing the Tape woudl she be aware of how to end the Calamity, though even then she took her god sweet Time telling everyone who The Dead One is.
Still, wouldn't the Calamity be easy to end at this point? Just send Mei tot he class every year, and she can point out The Dead One. Simple.
I also have to wonder what happened to Mei and Sakibara after the events of the show.