You just need to use your GM judgement. If you roll up d4 dragons(fairly sure i saw that on one of the encounter tables in KM ), it doesn't mean to say they are plummeting down on the pc party ready to fight. Have them hunting, and hopefully the PC's will think "shit, we should hide" then you could turn it into a stealth/chase type thing.
To be fair though i've GM'd on some parties that expect all encounters to be winnable, but nowadays i always prelude all campaigns i run with "You can't win all fights, running away and avoiding fights should be encouraged if it looks grim"