I just don't see two Forsaken acting in such close concert. Mesaana, Demandred, and Semirhage may have had a pact to work together until all other Forsaken were defeated... but as you get down to the last couple of opponents, that kind of agreement tends to weaken easily.

I can't see two Forsaken being willing to share their realms of influence... and a top general in the Seanchan army overlaps too much with Truthspeaker to the anointed future Seanchan ruler. Plus, what 'rule' in the Seanchan armies does Demandred have which is 'secure'? Fortuona as empress (or even Tuon alive and free, able to declare herself at any time) would certainly put the lie to that statement he makes to Moridin.

Demandred will be found elsewhere (end official prediction).