Am I obligated to report for duty if I have no orders?

You're an NCO and you have to ask this question?

What do the rules say, or regulation say? I would say yes.... But, like all things it comes down to the letter of the law, not the intent, in this case.

Despite not having orders yet, it is still expected that those on ADVON be present for duty as each of you have already been briefed on where to be and the time for your formation. Let the CoC dig a little more deeper into this and deal with the responsibility to find out where the processing and dissemination of orders in a timely manner failed. Chances are the ADVON may just be given their orders the day of departure while in accountability formation at 0530 hrs. If not, you were still at least present for duty and as a leader and NCO in your unit. The last thing you want to be held accounted for is missing your own ADVON flight. Not having your orders in your situation is not the right answer for those who were proactively engaged to ensure they had all blocks checked like you had done weeks prior but unfortunately this happened. Trust me, someone else will be found accountable.