Running away from a conflict is absolutely essential to a lot of styles of RPG play. It's common in real-life violent conflicts. But it's also nearly impossible in initiative.
But it's even worse in games with levels.
Monsters don't wear hats with their CR proudly displayed on them.
Uninformed blunder -> Fight too hard monster -> TPK = Bad!
Especially bad when the initiative system prevents you from retreating.
First, tell the players about the CR of the encounter they're going into, if it's too high for them. "Hey guys, the system says you'll probably all die if you fight this Medusa at level 2."
That sounds like roleplaying and story, not tactical board game communication. The players won't understand.
Because they'd have known going in that they wouldn't survive, and chose to fight anyway.
End initiative when the party decides to retreat. If one PC considers running away, ask them OOC if they're all going to retreat. If they do, drop out of initiative.
A hard choice
A skill challenge
A skill challenge: "OK, you're running? Group Athletics check!"
- Initiative and CR make running away suck
- Running away is absolutely essential to many styles of play
- Solve this by being open and clear about deadly challenges OOC and ending initiative once the players decide to flee.