The young Rat King did not care about the death of the Rats under his command, because he knew that these Rats generals and soldiers did not pledge their loyalty to him, but his father. Once they knew that his father was imprisoned by him, then his throne might be in jeopardy.
Therefore, these old Rats must die. As for the new generation of Rats, he had already made plan for it long ago. He left a group of Rats to reproduce in the cave. In just a short amount of time, it would not be a problem to have hundreds of thousands of newborn Rats.
At that time, there might be no more Rats who still remember the old Rat King. All the Rats would only know one Rat King, and that is him, the young rat!
Naturally, even if those Rats generals and soldiers were to give away their heads, he would not mind getting some benefits from the hands of different clans. It was just an act to recycle waste and gain something good out of it!