Felix stayed behind to prevent anyone trying to follow them from succeeding in their task. He did this by simply killing everyone who tried. Meanwhile, Julian continued the task of plundering the city.
Most likely, the city would rally around the support of a new leader after a few weeks, and if they were lucky, no beasts in the third kingdom would appear and they would be able to survive for a while. Otherwise, they would be easily decimated.
As soon as Kayden flew about 500 kilometers, he stopped in the air to take a short rest for everyone. The journey was relatively uneventful, as those in the second kingdom supported the weaker ones on Kayden's orders.