Unfortunately, a stupid leaf prevented me from capping Arthur, so we are currently lacking High King Peter, the Magnificent.

Arthur didn't leave with them, though. ;) He arrived later that night, probably had to sneak out or have Uther thrown him in the dungeons to keep him from helping Merlin; in Uther's (logical) mind, if Arthur was recognized and reported it wouldn't have looked good. Contrasted to Morgana, who left in daylight. I realllllly wanted to have an extra scene at the end of the ep getting back to Camelot and explaining to Uther where they'd been.

And I'm pretty sure Gwen and her father were already living in Camelot long before Morgana arrived: her father has a pretty big reputation for his craft in Camelot.