If Demandred has the Trollocs in place (can't gate them) backed up by a human army (more than Roedran) plus BT help, they'd be in great position in Murandy to capture central Andor/Caemlyn etc., bollixing communications throughout the westlands: cutting all roads, both rivers at least threatened, etc, etc.

Would make sense, but not a prediction. Countering the attack would be Andor troops plus some of Rand's legion(?) stiffened by Mat's Band, perhaps all armed with the new crossbows. Some aes sedai at least, and perhaps reinforcements from the White Tower and Rand to add to the cannon. First use of massed cannon fire (with or without shells, but I expect with), combined with, hopefully, horse artillery (small mobile units firing grapeshot or small balls to break up formations during assaults or the heavy cavalry charges) might just equal power wielding fighters, before counter measures could be developed.

Elayne's position in Caemlyn seems very precarious, however. Too many DFs, BA etc captured and loose, probably Moghedien, etc. Needs reinforcements from Rand and especially Egwene (who in this scene was probably still a captive).