In my campaign the bbeg has a powerful henchman that goes around doing his dirty work. Lets call him greg for the post. My players have had multiple encounters with greg to progress the story and give a bit of a display of power. So far either Greg has had to retreat because of massive reinforcements coming to the players aid or the players have had to run from an enemy that's obviously beyond them. It's lead to some pretty fun encounters and some beloved npcs have died covering their retreat. My issue is that after these repeated experiences I have a feeling that when they are powerful enough and it's time to fight him they will only be thinking of escape. How would you subtley let them know its go time without breaking immersion?