That depends upon one's perspective. Personally, I wouldn't say that much of "modern Black Metal" is Black Metal in the slightest, and I know that many people argue that Black Metal must be Satanic, or they argue that it can't have keyboards, or that it uses this, that, or the other technique, or that the Norwegians usurped the name of the genre while playing something very different, etc. If Black Metal is a style which was played ten years ago, or twenty years ago, and is now merely mimicked, then it's pretty dead.
On the other hand, many people would say that a musical genre can evolve, just as a band's music evolves. If such is the case, then, given that most bands whose sound "evolves" end up being pretty crap (Darkthrone, Immortal, Mayhem, Enslaved, Emperor), it stands to reason that the evolution of a musical genre must be pretty crap as well (though this may not be the case, I'm extrapolating a bit here). I'm not sure if "being generally crap" constitutes being dead.
The audience, certainly, has changed. Where once the music was appreciated by a select number of souls whose knowledge of its existence was almost entirely the result of their search for such music, nowadays, any moron who hears Cradle of Filth or Dimmu Borgir on MTV can jump into the wonderful world of "Black Metal". In a small number of cases, people progress beyond this exterior; in fewer cases, people reach the true gems of the genre.
To respond to your earlier statement, it is not "simplicity", but, rather, "the appearance of simplicity" which is prevalent (in some cases) in Black Metal.