I think 2B and 2C are, again, out of the question. The madman has opportunity for subterfuge and deception; so why would he do precisely the thing that he most obviously looks like he is doing, that is, attacking Odessa with all his might? He knows that a noble with no military experience has just taken over a group of demoralized soldiers waiting for an excuse to retreat; wouldn't he expect us to come to Odessa? Sure, there's an outside chance that there is something important in Odessa or he is going on an Attila the Hun style march into the heart of the Empire, but we can't rely on long-shots like that.
So the only question is, do we go for AAA2, going all out for Tigrien, or ADA1/2, and going with a thousand men to scout out either Odessa or Tigrien with Garsu? The first has the prize of achieving our primary goal, and the risk of, well, losing everything. The second has the prize of more information (and possibly nullify all of the Madman's deception), but will probably mean we will be too late to either save Odessa or Tigrien. Not having heard from the fort doesn't mean they're all dead - it might just mean they have nobody courageous or able enough to sneak past the Rus in the wilderness to get us a message, which I think is a reasonable assumption. If Tigrien really was wiped out, it would represent a massive, massive victory for the Rus and the madman; what would make most sense for them to do then is announce the news, chuck dismembered heads at our camp, parade with Ban's head on top of a stake - really demoralise us and make us retreat altogether, upon which they would ambush.