After dealing with the President, there wasn't much Ashton had to do except one thing. Corpsification gas was running rampant in the atmosphere. As such, most of his forces couldn't enter the cities.
Moreover, the barrier encasing the gas could disappear at any moment. If that were to happen, tons of smoke would escape into the environment. Ashton didn't even want to imagine the catastrophic results of such a disaster.
While he could release the cure in the air, just like He had done in Contingency, it would lead to the annihilation of the undead altogether. Despite his rage, the logical side of his mind refused to commit genocide on such a scale.
"Bismark," Ashton called for the lich, "Gather everyone and consume as much smoke as possible in fifteen minutes."
Thankfully, Ashton had his undead to support him. Consuming the gas would permanently increase their stats by leaps and bounds.