Yes, it would have been grounds for a mistrial. Someone will correct me if I'm wrong (going by memory), but I think the DNA results were consistant with blood coming from either Jason or Steve Branch. I do not think Damien's profile matched any of the blood tested on the pendant.Jason's attorneys were looking for any possible reason to sever the case, and probably would argue that it prejudices them since it is strong physical evidence against only Damien. Damien, on the other hand, would want to argue that it was Jason's blood on the necklace and/or that Jason was the one who was wearing the necklace around 5/5/93. As a result, the trails would've likely been severed. The State would not want that, because it would dramatically decrease their chances of convicting Jason.
It hasn't been destroyed. There isn't much of it left, but they don't need as much now as they did back in '93-'94. When you said that it is too late for 'them' to retest it.....................your referring to the defense, I assume. The prosecution has nothing to prove, and no need to retest. The defense certainly does not want that pendant retested. I assure you of that.