Whoever ordered the military to not send help is who is finally at fault. It had to be Obama or the Seals would have been there and likely nobody dying.
Dempsey is not technically in the chain of command but Panetta relied heavily on his Joint Chiefs. My suspicion is Dempsey advised that the situation did not justify military intervention and Panetta never elevated it to the President. I am confident that Obama had made it clear to Panetta that he wanted “plausable deniability” if anything went south. I do not trust Demsey any more than I trusted Mullen.
I doubt any military help would have stopped the initial attack. We should never have been there in the first place. The cardinal rule of diplomatic security is that you don’t go places where the host government cannot protect you.