Based on what Roy said, they were likely counting on Xykon to break in, grab what he wanted, and leave with his prize; without having much time to bother with the rest of the city...at which point they would come back and reclaim their stuff (and possibly more, depending on how Hinjo's ability to resist was looking). Xykon being unable to take his prize with him, and thus hanging around the city with an army of hobgoblins, would change that picture.