Re: TNG Cold Equations Book 2, Silent Wpns Nic-Picks -- SPOILERS
Every commissioned officer is part of the command structure. When all senior officers are unavailable, usually the highest ranking officer takes command, whatever his position. But this may be more of a guideline, rather than a strict rule. We've seen Sulu in the chair with McCoy standing by.
1.000 years: University Leipzig, 1409-2409
Gorn to be wild!