Interesting theory...
...but that barely stops it from being crap. the lyrics to the song are just lyrics, they dont mean anything. and the pictures in the booklet hardly count. bands have pulled off things like this before, putting clues in songs that lead to a band member being dead, but they never say it right out, or draw pictures of them as zombies. they would never be so obvious. the beatles did this with paul, except they would put things like open palms over paul's head (which is a sign of blessing to the dead), or a tape of a car crash played followed by paul's voice saying "let me out! let me out!" - backwards. the zombies were just booklet art, and the grim reaper thing might have just symbolized the rest of the group fading away from music.