I'm very sorry to hear that the puppy lost his life, and I really don't want to sound insensitive, but seeing the situation about the puppies (in a previous thread) was shared, I feel the need to be a little honest...
I really don't think that the breeder had any sensibility about the puppies, and it sounds as there was no business to even go to this person to for a puppy. And a lot of people treat the words "they love their dogs" as the same as saying that they give them proper care. Anyone willing to sell, and to be perfectly honest, bring home a puppy 6 weeks old, is probably someone who should be making much better decisions.
Now, I do respect that you took advice and gave the puppy back, but then this happens and I'm left with a very sick feeling in my stomach. And maybe this is insensitive and petty, but "It was playing and it fell off something and hit its head or something I dont know all the details yet.." seems less that the response that would make me feel comfortable about the situation.
I care for all of my animals well, but my dog is genuinely a part of my family. Should something this tragic have happened to her -"it hit it's head and died" would be such a disservice. Dogs are the most amazing creatures on earth. Mistreatment, negligence, or even a lack of understanding on caring for them is unacceptable.
If I sound like a heartless jerk, I apologize. But this situation, as I read it, was a questionable one from the start. I was unsettled by the first thread, and this conclusion raises more doubts.