Run away from combat? Hell, it was a major point in my last storyarc for 3.5 - three level 12 charcaters went into a cavern supposedly beset by a clutch (as in MULTIPLE) Shadow Dragons. I let the players catch the beasties sleeping so to afford them a way out, so they could come back later (there were still a few story elements I had placed for this scene), BUT NO! The rogue/barbarian in the group sneaks behind the biggest on (a CR 17 - I forget which age cat) and tries to Sneak Attack it. He got a Crit, and the melee engaged.
After they lost two characters, the barbarian/rogue rages, and manages to polish off the remaining Dragons (three solo kills - all flat-out luck of the dice, I swear!) whereafter his Rage ends him with only a single HP...
Needless to say, the party sat for a while before everyone could be rez'ed...
All because the group thought "hey, we can take 'em." and they didn't take the hint to run. Geeze, if only my dice would love me as much as they loved Matt's Rogue/Barbarian....
An interesting postscript to this story is that they tracked down an Ancient Red (you read that right) at 15 level, and they assume it's there for them to fight....
Fancy dice rolls WON'T save them this weekend...