Main question is: "Was it preventable."
And the answer to that was yes, in some manner, yes. If not completely preventable there was plenty of warning that could have limited the damage and that it was policy from the Clinton lead state department (if not direct orders from her, but we'll likely not find that out due to the email issues) to make it seem as if everything in Libya was going great. Libya was Clinton's baby and even when it started falling apart, the idea was to keep up the show that it wasn't. More security at the embassy would have been bad press and contrary to the narrative she was pushing. Pulling out from the embassy would have been bad press and contrary to the narrative. She or someone working for her with her instructions risked lives in order to further her career and keep up face. You could give them the benefit of the doubt if they'd listened. If they'd assigned more security. If they'd done SOMETHING. Hell, you could give them the benefit of the doubt if they even had the basic minimum security there that is mandated by their own policy. But they had less than normal security there to keep things low profile. To make it seem like everything was great and dandy and that the Libyans loved them.
Now, as far as I'm aware, there is no proof that any of this info passed in front of Clinton's eyes. As far as I'm aware there's no proof she gave any specific orders which doomed the people at the embassy there. But she was in charge and poor decisions were made somewhere along the line and it's a fair question who made those decisions that cost people their lives.
Now... was it blown out of proportion? Was it turned into a witch hunt? Did it take far too long?
Yes.
Yes.
and Yes... although it must be said partially as a result of Her and her staff's uncooperativeness.
The end result was that she, or someone working according to her wishes screwed up royally. If it were her, I'd say that should disqualify her for any further jobs in government. If it were someone under her, I'd still say that shows she can't keep track of what's going on in the world (especially in a hotspot she'd spent so much time poking at) and should disqualify her from at least anything involving international relations. (Including President.)