Pride and Prejudice and Zombies didn't in any way damaged or removed anything from Pride and Prejudice though. The book is still there for everyone to enjoy.

The movie was also a commercial failure, I'm not sure we would end up with so much junk if it doesn't sell.

Would we? You can do that now because parody is exempted from copyright, so there's not much preventing you from doing Zombie Lord of the Rings or whatever (Tolkien parody works already exist, eg Bored of the Rings).