What the story needed [SPOILER]

[Harry]

Well, it sounds like they die, but then again, the grunts do kind of look like parts of them 'exploded' which might fit.

I know they use people to steal others, but In my mind, the grunts originally were used to steal humans but replaced because Alexander felt men such as Wilhelm would do a better job.

I'm guessing mindless zombies ask a lot fewer questions of Alexander, what with him being hundreds of years old and all. Not being questioned like Wilhelm does would have its benefits I'm sure.

I'm happy if the origin of the monsters isn't explained, as you can read as much or as little into it as you like.