Well, my Japanese is not that good, but the one who posted the webpage said something like this about the book -
'Alex's death in the end was was unfinished mystery, whether he is dead or alive.
'In conclusion, Alex is alive. Banzai'

(she said it, not me)
'But the anime's circumstance is completely different... so the ending is rather strange. No, maybe death would have been better' (not very sure about this, I'm somewhat confused too.'
'In addition, the place where Klaus lived (?) is indeed Earth.'
I have no idea what this book is, whether it's a novel tie-in, a re-write of the TV series, a continuation, or something else. Maybe the original poster can elaborate?
I still stand by anime's rule - 'if you don't see the corpse, s/he's not dead! And even if you did, s/he may still come back to live.'
... and then again I may simply still be in denial over Alex... :blue: