Someone played Of Power & Glory and had a bad experience with it. As I understand it, in their game, 3 kings were killed very early. Of the remaining five kings, two were small and therefore not involved in many battles. The other 3 kings had all of there titles taken so the game ground to a halt.
I suspect this is a rare situation since I've never encountered it, but I do want to do something about it. My current solution is to make the following rule change:
If a King needs to expand into a territory and there are no rings left, but there are rings on some of the nobles in his court, take a ring from the noble in the 1 position.
If that rule were in place, then the game would not have ground to a halt. The three big kings would continue to expand as the title collected from them by the players get eaten up. Here's a little math on the subject: there are 24 territories and each King has 9 rings available for expansion. So with only 3 kings, that's enough for all 24 territories (and then some). Even if you only had 2 kings, that would be enough for 18 of the territories. And if there was only one King... then the game has bigger problems. I'm not sure if I should protect against that or not. It may be such a rare thing that I don't worry about it.