If this expansion is a 2hr to 3 hr movie... The ending would be like...

WoL would be questing to kill lightwardens. While Garlean plans an all out attacks.

WoL trying to defeat Emet while struggling with the light corruption.
In the source, the alliance of eorzea at blink of defeat.

WoL finished of Emet and gian control of new power. Able to command an army of sin eaters.

WoL returns with an army of sin eaters n win the war. Final showdown with Zenos.

WoL wins. As usually... Scions will appear at the end. Then happy ending ever after.