Actually, you kinda can still leave the whole area and back to the scrapyard right before you fight Titania, Of course that means you'd have to progress through her gym, wake up in a tower, fight "The Dragon" and reach Titania.
Basically, instead of fighting her immediately, jump down the hole behind her, go down, follow the route to the left and you'd be back in the scrapyard. Don't bother going back out via the first time you enter "Once Upon Somewhere"; you can't.