People have mentioned Loghain as someone who should have been your military commander that wouldn't make a lot of sense for me given he died in all but one playthrough.
I doubt your advisors can leave or be killed simply because you need them for the war table to function.
I do find it strange that people hate Cullen for being anti-mage when given his history it would make no sense for him to be otherwise, he was tortured for weeks (perhaps months) by demon possessed mages, after that he was posted to the worst circle tower in Thedas and had a lunatic as a commanding officer......yet it appears he's worked through his problems and was highly thought of by the Divine (who was pro-mage), he has stayed loyal and abandoned the Templar order.