Absolutely, Marines would have protected their ambassador. No doubt about that.
The next question is (and I don’t have the answer) why in the heck aren’t they using Marines? Too offensive to Muslim sensiblilites maybe? If I was an Ambassador in a foreign country, especially one with recent war/strife going on, I would want my own country’s military protecting me - I know they would die protecting me, not tipping off the enemy as to my whereabouts. What a cluster you-know-what.