A screwjob? Really?
Plot-wise, I think the most likely thing is for Wanda to lose this. I continue to think that the main factors in this will be
1) relationship-wise: Wanda being overconfident in her ability to understand Jillian. I suspect Jillian will be able to lead Wanda into some sort of trap.
2) battle-wise: there's a MYSTERY CASTER. We know how powerful casters can be. The mystery caster will be revealed to be some type of caster we haven't encountered before, and it will turn out that Charlie picked this caster specifically for this sort of battle, and it will make a big difference.
There's enough leeway in those two things to write a very good story that involves Wanda losing, or at least not winning. It can be made into a close fight, which can justify Slately not being croaked until Haggar steps in on the next turn, if at all, giving him time to name Trem as an heir.
Quit being so pessimistic!
(Though I do hope that "hidden archon army" isn't what changes around this battle. Yeah, it's possible, but it seems like such a blunt instrument - Charlie does finesse and manipulation, not zerging with archons. I could buy one or two archons that help somehow, but not the "army appears and overwhelms Wanda via numbers" option...)