What happens if you exit chargestone cave without battling mr n when you try to get back were you were before bianca and the profesor are blocking you?

If you exit Chargestone Cave without battling N, you won't be able to re-enter the cave from the same spot. When you return, you'll find that Bianca and Professor Juniper are blocking your path, preventing you from accessing the area again until you've completed the necessary battle with N. This situation is designed to ensure that players progress through the story in the intended sequence.