Yes. Pure and simple, dogs can and do die from eating chocolate.
The compounds that cause the issue are Theobromine and Caffeine. Each of these wreck havoc on a dogs nervous and cardiovascular systems.
But how likely is your dog to die? That largely depends on a combination of factors:
1) What type of chocolate did your dog eat? The darker the chocolate, the less of it is needed to do your pup in. We discuss the different types of chocolate and their comparative toxicity here.
2) How did your dog eat?
3) How much does your dog weigh?