Well if there aren't morale rules I'm house ruling them in. Having this kind of rule is important (at least for how I want to DM) for communicating, "I am an uncaring god, I care not if you live or die, it's all up to you" to the players. If the players manage to spook a giant lizard that's about the eat the cleric I want them to think, "damn we were lucky" not "damn the DM is going easy on us."