Let my throw these thoughts into the ring...
"When in fear, when in doubt, run in circles, scream and shout!"
In Stormbringer, Call of Cthulhu, WFRP, "cool" checks were the norm such that it seemed nothing out of the ordinary to have half the adventurers running in panic and trying to 'escape'. In fact, we probably had more "fun" trying to role play the panic than actually 'standing and fighting'. Admittedly, we had a number of loony players (including yours truly).
In RMC, D&D, we panicked and ran all the time because we opened the wrong door or blundered into something dangerous. Obviously, demons and undead cause failed fear checks and result in PCs fleeing in fear or worse the draft horses flee in panic taking half the adventurers down a dangerous mountain road in the wagon...
As a Gamemaster, I often test the players 'mettle' by giving them encounters where the best possible survival option is "RUN AWAY! RUN AWAY!". Most of the time, they remember that fleeing in panic or making a tactical retreat is a perfectly valid encounter option. Sometimes, however, it gets a bit ugly...
So. Morale checks? If the best fighter goes down, should all the PCs have to make a morale check if they don't bother to flee all on their own? Maybe. Maybe not. It seems perfectly reasonable to me. Then again, most of my gaming groups were always conditioned to panic all on their own - and so we would flee without GM prompting. It sure creates hilarious plot complications when a panic arises.
