I agree that if the host country cannot guarantee the physical safety of the embassy personnel or grounds then we should not have an embassy there. The question then becomes what do you do when the host country guarantees that safety and then something happens? I think it is best to see whether the host country (1) publicly and strongly condemns the attack, (2) makes a good faith effort to find the perpetrators including sharing all information they have with us, and (3) helps us in our effort to ensure it does not happen again.
I think we are going to be dealing with a lot of problems with both sincerity and competence among the factions of these new governments. Just pulling out and leaving them to stew in their own juices is a recipe for failed states and Taliban-like fundy movements. As irritating as it is, we have to stay engaged.
Short of turning the entire region into a parabolic mirror, that is. I imagine there will be calls for that eventually.