Possible outcomes from my perspective:
1. Stanley stays and fights in GK. This could lead to the city being destroyed, thus destroying all units dependent on GK for upkeep at the start of the next turn after the destruction. I'd give this one P<0.01 of happening, since Stanley already considered fleeing--and most of the treasury is gone by now anyway.
2a. Stanley flees, but Parson/Wanda stand and fight, possibly ordered to cover Stanley's retreat. Since the summoning spell will end Parson's existence if he refuses an order(See panel 7), he'd be stuck doing just that, likely causing the destruction of GK and himself...Wanda might switch sides, however. Note that if an objective of the allied forces is to hold GK intact, then Parson could coordinate guerrilla tactics in the streets.
2b. Stanley flees, leaving no orders for Parson, Wanda, or anyone he doesn't take with him. This leaves Parson and Wanda as essentially free agents, able to negotiate or surrender, thereby maintaining their existence.
3. Parson's next stupid meal...does something mind-bending. I don't even want to think about that, since it could literally be a deus ex machina.
4. ...the authors do something within their ruleset but that nobody thought of...which seems to be a pattern with this comic.
It's also worth noting (someone referenced that Parson, Wanda, and Sizemore may be unable to speak again) that Stanley only said "Don't say another word in my presence".
Interesting days in Erfworld...