Vandalieu had several contingency plans in mind for handling the Sauron Duchy. The ultimate decision, however, rested on whether Elizabeth wanted to take on the responsibility of the Sauron Duchy or not.
If Elizabeth wished for it, it would mean she hoped to protect the duchy and ensure its safety. If she didn’t, it would imply she was indifferent, feeling that it wouldn’t matter what became of it.
In the case she didn’t care, Vandalieu and his allies wouldn’t go so far as to actively destroy the Sauron Duchy or lead it to ruin. Naturally, as a follower of Vida, the goddess of love, Vandalieu would never willingly trample on innocent lives. After isolating the former Scylla Autonomous Region, they would likely just conduct typical activities there, like Kanako’s live performances, Darcia’s visits, and Vandalieu’s guidance, disregarding the fact that the Sauron Duchy bordered the hostile Amid Holy Kingdom’s vassal state, the Mirg Shield Nation.
Should a war break out with Amid’s forces invading from the Mirg Shield Nation, they would respond appropriately. They would aid the Orbaume Kingdom as an ally, sending supplies and arranging reinforcements through the Adventurers’ Guild. But that would be the extent of their involvement.
They wouldn’t dispatch Knochen as a moving fortress, nor have Borkus and Vigaro wreak havoc on the front lines, nor use Sam for transporting supplies.
Of course, they would spare no effort to protect the people they had guided, and they would help reclaim any occupied lands from the Amid Holy Kingdom. However, by that point, the Sauron Duchy’s government would likely have fallen.
Vandalieu felt no value in Rudel Sauron and his faction, who had abandoned the ‘Liberation Knight Princess’ Iris and the resistance. For him, with his allies like Gufadgarn, who could open [Teleportation Gates], and Quattro and Sam, who traversed the skies, the Sauron Duchy wasn’t necessary for his impending confrontation with the Amid Holy Kingdom… or for his inevitable battle with the Lawful God Alda and his champion, Heinz.